Pros:
Insane damage early-mid game
Good survivability
The best hero to get first blood with.
2.5sec silence
900 gold worth of free Armor and MR
manaless
You are a badass

Cons:
Lacks CC
Close range
Stuns and snares hard counters Garen.
Heroes like ashe can kid you all day long.

Garen
Welcome to my Garen guide. This is the first time i write a guide and i do this cause i want people to understand Garen's potential as a tank and dps the same time. Garen is not to be player ether full tank or full dps.
Why that? Because if you go full tank then you wont be much of a threat late game as you wont be doing much damage plus you will be wasting garens potentials.
Now again if you go full dps you will just die too easily in team clashes and you wont to live long enough to ulti the other team Cho'Gath and chop to pieces that Ashe.

Now as for the items i listed i tried a lot of combinations for Garen in order to maximize his tanking ability, the ability to withstand tower camping (spamming) and have the maximum damage output in all stages of the game (early to late game).
In most of my games the game ends as soon as i make my Atma's Impaler or even sooner but if the game last too long then this should be the final item build with your core being Ionian Boots of Lucidity and Sunfire Aegis however don't hesitate to change the items based on what the enemy team has.
For example if they lack magic damage or champions who can easily build Madred's Bloodrazor as there core which will be your main fear with this build or until you grap some mr at least you can skip Force of Nature and make Phantom Dancer for more damage and movement or even last whisperer if that enemy rammus keeps taunting you cause you got overfed ;p

Ok enough with the introductions. Grap your boots 3 health pots and go to line with your 31 armor penetration. Note that if the enemy team has a jungler then you are a good hero to skip the 2 health pots and grap a sight ward to ward the enemy blue buff for an easy kill since your passive will do most of the healing.
Prefer champions with crowd control spells or champions that can dish out some early damage for total line domination. One champion i personally prefer is your sister Lux with some mana regen runes.
With your passive and 3 hp pots you can out-endurance the enemy champs and force them to stay back and deny them the creeps or come forth and taste your Judgment. However if there is an enemy healer in line be careful how you manage your hp, try with your partner not to push the line and burst him to death at lvl 3.

Hide in bushes and wait for them to come close spam them with judgment when they do, if there is someone fool enough to come in lane with you with less than 450 hp you and your partner can easily fb him at lvl 1. In 70% of my games me or me partner get fb and in 80% of my games i totally dominate my line. Do not push the line instead hide in the bush for your Perseverance to work and come out only for a last hit or to silence and spam that Veigar who came to Baleful Strike.

Usually the first time you will just take away 2/3 or 1/2 of there hp and the 2 time they come close you will kill them but always be careful do not push the line to much and do not tower dive! I have seen my lines getting destroyed cause my partner was too greedy and went tower dive to grap himself a kill of the below half hp enemy champs that i was spamming. If your partner decides to tower dive dont be fool enough to follow him at lvl 3, you are no match for that tower..yet. Always use your mind first, however at lvl 4 that you get a skill on Courage you can withstand 1-2 hits from the tower but still try to act properly in each circumstance. Do not allow yourself to give away free kills, remember you are a pro xD.

As soon as you hit lvl 7 try to find easy targets to gang. If that enemy Karthus mid line is pushing hard and you have your summoner spells and ulti up dont be afrait to go and grap yourself a kill, remember that once you get close and personal with him or any other spell caster who relays on his spells and silence him he is at your mercy for 2,5 seconds and by the end of this time he will realize that his half health is missing he will be trying to find an escape mechanism, chop him a bit more with your autoattacks (they do some damage too ;p) and send him back to his fountain with your sky sword.

By now you should probably got at least 1-2 kills from your lane or at least some assists and got your core. Try to spot where that 1300 hp enemy teemo is and kill him with your combo. Ghost in, activate Decisive Strike as soon as he spots you and starts running, Exhaust him when you get close, silence him Judge him and send him back to the fairy land with your flying sword again xD, NOTE that if you are not lvl 11 yet you will need some auto attacks before you ulti him.
Now at this point this is where team slashes and tower camping begins. try to avoid getting over-spamed so your passive can heal you and prevent running back to fountain, also try to find some time and chop the nearby wraiths to get 2 armor and mr for your Courage plus the extra gold.
When the fight beggins if you are caught in the middle the start judging the most you can, if not the run in and silence the most dangerous spell caster before he use his abilities or that Vladimir who has low cooldawns. Activate courage when you became the focus and try to run a bit back or spam a bit more depending how much more you can still tank, ulti the first high hp tank who gets low or any low hp enemy champ who starts to run away and always make sure your ulti will grap you the kill.

After all that hard lane time you gave to the 2 enemy champs, all the kills you stole ;p, the punishment you took for your team and the game has not ended yet? Did you get overfed and got all your 6 items then charge in get a tripe kill or something and try to finish the game ;p
Just be careful thou as clashes here will determinate the game, don't be Marco Polo and go exploring bushes instead try to ward them, get the nashor if you haven't already and keep in mind that your team might not be as much overfed as you, remember? you stole there kills ;p (that's how it works kids)
If the enemy team got nashor it might be best to play defensive until they make a mistake or it wears off.
Also keep in mind who you will silence and when to open your Judgment and who you will ulti as everything is crucial from now on.

Play Video

Here are some extra notes you might want to know when playing Garen.
1)Armor penetration will not drop your opponents armor below 0, so for example you have 31 armor pen and your opponent has ether 11 or 31 armor you will still be doing the same damage.
2)You cannot lifesteal from your abilities but you can however spellvamp from them however i personally dont think you will benefit much from making a Hextech Gunblade, it is better to ask your team to make Will of the Ancients. Also note that multi target spells work at 33% of the listed rate such as your judgment so to spell vamp that 20% you will have to hit at least 3 enemys.
3) Demacian Justice can be blocked by Banshee's Veil
4) Decisive Strike can be used to deal some heavy damage to turrets but the only dilemma is use it to damage the turret or save it to run away when the enemy champs realize what you are doing xD
5) Decisive Strike resets the Attack-timer upon casting it and upon using it so you can do 3 fast attacks. (autoattack - activate Decisive Strike and hit - autoattack again).

Thats all for now pls try out my build and post some comments, i am looking forward for other people opinions, also i will keep this guide updated and add more info as soon as possible.

Thanx a lot for reading my guide.

26/1/2011: Added pros/cons
31/1/2011: Added the champion spotlight
3/2/2011: Modified a bit the guide for easier reading