This is NOT a tank guide for Malphite! I cannot stress enough that while he is a great tank he is an absolutely terrifying champion to play against with this item sequence. However please note that even though this is a very successful build, I only play it in about 60% of my games as Malphite as you see it here. For the other 40% you are easily able to substitute more MR to cope with the unusual cases when you can't rip off a squishy mage's face in less than half of a second.

Note: I apologize beforehand for the lack of pictures found in this guide. It is simply a text document with no fancy efforts. If you would prefer pictures then leave this guide now. If you think Malphite is only a tank, then leave now.

Note: If you wish to jungle, then you only need to change one thing about this entire setup, switch one mastery point from your "Archmage's Savvy" into "Plentiful Bounty." This is a minor change that will just make your jungle routine a little smoother with a slight increase in benefit. Also I will not go into great detail about jungling with him unless I have a large group ask me to add to this guide.

Malphite's ultimate requires the cooperation and attention of your team nearly every time. If you feel that your team will not do a good job of this, play someone else as it could seriously hurt your team as your ult could be useless.
Always pay attention to the map and in team fights to who is doing what. Your job is largely to control the fight even more than it is to tear people's faces off! Even though you are not a pure bread tank it is still your job to protect to your fullest capacity. And usually it is in you and your team's benefit to do this as it allows for even more damage on your end to be dished out while less from their end.

Pros -
Passive shield allows for longer lane survivability
Great harassment with Seismic Shard
Really good move speed with Seismic Shard
A Rank one ability that boosts armor and damage by 20%
His E does damage augmented by his Armor.
His R is the best initiator in the game, just think, jump in and knock them all up while tearing their faces off. Any get away? Chase them down and tear their mother's faces off too.

Cons -
You miss his ult, less ripping and tearing of faces.
Cannot excel in 1v2 lanes in an aggressive face tearing play style, he must sit back take the hits which he doesn't like. Keep him paired with a strong early game ranged carry such as Teemo or Caitlyn.

Note: Malphite is very depend on his team on many occasions. You need them to know what to do when you ult in otherwise it could be a wasted opportunity. Also note that when Malphite doesn't get to tear people's faces off, it becomes difficult to excel with him in this role as his final build has a cost of just over 14k to pull off.

Now briefly I will touch on why I took the runes I did and a few alterations that can easily be made and will still be effective.

Original -
Quintessences: +78 health is the ability to tank two more hits at level one which is huge if you are forced to 1v2 against ranged carries.
Marks: When you have an extra 15 armor penetration at level one it means you will be cutting through half of a squishy's resistances and about a third of a more tanky resistance. This is huge as it will help your early game and late game as you won't be building any other armor pen.
Seals: Taking an extra chunk of armor is always acceptable when you want to rip people's faces off. If you build these then you may just find it easier to rip people's faces off. Did I already say how fun it is to rip people's faces off?
Glyphs: I take MR/level because they add an additional 25 MR at level 18 that this build needs. Without solid runes augmenting your MR you will find yourself dying quickly even with your 4.5k health.

Another Option -
Seals: Switch out the armor seals for flat health seals. This will add a little less than 50 health to your health pool which is just another hit you can tank from that annoying Caitlyn.

Another Option -
Marks: Take those armor penetration marks and replace them with magic penetration marks. This will mostly help your early and middle game while not doing much late game. Your Q should be maxed out first because it will do around 200 damage and it is easily spammable. It also works really well if you follow my setup for masteries.

There is really only one way to take masteries that truly works with him and augments all points of his game. By taking 9/0/21 you will have really effective damage with your Q which is essential as his only ranged ability and especially so if you are solo laning. I focus on utility because while Malphite has exceptional damage output and is very tanky he still needs better mana regeneration and even more chance to tear people's faces off using Flash and Teliport. Flash is a must have with every champion because it will both save your life and end the other teams lives due to the instantaneous aspect of it versus Ghost.

Now specifically to summoner spells. You need to always take flash. I cannot stress enough how many times it will get you another face to add to your collection while at the same time keeping your face from being added to another person's collection. At the same time I really like taking Teliport. I take Teliport for two reasons. One, it means you can leave your lane for 5 seconds to purchase more tools of face destruction. Two, you can teliport to a ward hidden in a bush and ult on the guy that just checked the bush thinking it is safe. Surprise!

Never take any other spell on him unless you absolutely must and the only other options would be Ignite, Exhaust, and Smite. However only take Smite if you are jungling.

Note: If you choose to jungle always go Flash/Smite. For jungling route start at the top and work towards the bottom. (Blue, Wolves, Wraiths, Red, Golems)
Note: While exhaust is a great spell to have, it isn't always a good choice on Malphite due to his Q. Your Q has a move speed buff that scales off of the target's move speed which means that if you choose to exhaust and Q them your speed won't be quite as fast as it could have.

Like I mentioned earlier Malphite has a situational build style. I will begin with the order of building that you will always follow with the build I have listed. Begin with a Meki Pendant and two Health Potions. This will give you plenty MP5 to hold your own in the lane. Stay in the lane as long as you can. I consider that once you have saved around 900g you should head back to base and purchase the Chalice of Harmony and tier one boots. These two items give you such high sustainability at this point in the game that it will be hard for anyone to push you out of your lane. Now it gets to the question of when do you leave your lane again. Generally around the time you hit 900g you will be level 6 or close to it. This means that you can gank other lanes or dominate in your own lane. As soon as you can finish your boots which can be either Mercury Treads or Ninja Tabi, based on both the composition of the other team and their performance. (If their team has two AD like Master Yi and Tryndamere, yet both of them are really bad...don't worry about Ninja Tabi, go Treads. However if they have a heavy AD team that is doing well, go Ninja Tabi, they work wonders.) Your next item should nearly always be Sunfire Cape. Start with Giant's Belt preferably but it is not essential. After finishing that move on to Warmogg's a.s.a.p. This will jack up your health both naturally and through your passive. Atmas should come next. What you build first for this combo is completely situational. If you aren't dying a lot and need some more damage, go critical, need to be more tanky you should go with the armor. After completing Atma's you should be in a position to be nearly unstoppable even with three people pounding on you. Now for the final item which is like adding a third arm, leg and layer of rock. Trinity Force. Ever seen a Malphite screaming at you with three arms three legs and a belly? It is like hillbilly that lives next to the power plant thinking it is a booze store. You will be critting for close to 1400 damage every other hit while making that Tryndamere cry wishing he could be you. Too bad....he now has no face.

Note: You can get rid of Atma's and Trinity Force for other items such as FoN(Force of Nature) or BV(Banshee's Veil) and such if you wish to get more survivability and your team doesn't need any more damage output.

Skill sequencing is essential if you want to pull off a successful Malphite. It is hard to simply write out an order but it is essential with this build that you max out your potential in Seismic Shard. This is your long stick with which you taunt the other team with. It does enough damage early game if used properly to tear one of their legs while you get to hold on to it for a while before beating them with it just to show them how insignificant they are in your presence. Level this up every chance you get.
Most importantly though is your ult. This is an obvious choice to max out as soon as you can as well. A well placed ult will incapacitate two to five members of their team. Remember however that you have to pick and choose with your ult and it is very situational. If your squishies are getting shreded by an AD carry, activate Brutal Strikes, ult on them, then proceed to ground slam. They will be in the air, lose half there attack speed and health. If they still insist on chasing a squishy use your Q on them to stop them.
Second you have will level your E. This is an essential second pick as it does crazy AoE damage as well as nukes a third of their attack speed. After leveling your Q again you will have to make a choice between your Brutal Strikes or your Ground Slam. I usually put a point in Brutal strikes because that free AoE always comes in handy as one punch can add three faces to your collection. At the same time it gives you a 20% armor and attack damage buff that works well with all of your abilities. These two abilities are tertiary but are very close in equality so will have to be individually determined by what you need to augment your game and help your team.

All of Malphite's skills have synergy with each other, only practice will help you to learn the best ways of working through each situation.