Gangplank was my first big purchase back when I was low level. Who wouldnt want to be a pirate with crazy kraken chest hair, amiright?
I soon fell out of love with him and cheated with many other champs before deciding at level 30 that I needed an AD champ to play.
My first game I went 23/4/7 I felt all my lovely feelings returning! Oh pirate you have pillaged my heart!

Pros:
Fast: you will notice I don't include boots yet I don't have problems chasing down enemy champs. PD gets you close to 380 by itself! Add Infinity edge and a second PD and you can book it.
Massive damage: I crit for over 700 late game every 3 second. every hit is around 450.
Map control. Your teammates at bot need some support but you are top? You have your global ult. Not a lot of damage but enough to turn the tide with the slow and damage. It also freaks people out and can push or defend creep waves w/o requiring you to run down.
Farmer: easy farming with parley early game
Cleanse: what kassadin I'm silenced oh wait nope! Rune prison ryze? Not today sucker.

Cons:
Squishy: oh so squishy! You end up with2500 life but you die fast you have to have map awareness and know when to run.
No hard CC: and only his ult for soft CC. You kill them quick or you chase em down.

Now a lot of you guys are gonna be wondering why there are no boots in this build and i will tell you. You don't need them. Everything you get from boots can be easily gotten else where at slightly higher cost but with much better late game utility. But we'll get into this later.

So explaining the skill sequence: Starting with the Brawler's Gloves to give you some initial crit chance. After you upgrade that to Zeal you'll have spent about the same amount you would have for any pair of boots. Berserker's Greaves cost 920 so that is about 250 less than Zeal at 1195. The boots add 70 MS and 25 AS. for slightly more you get 20 AS 10 crit chance (which is the most important thing on Gangplank and +8% movespeed. Now assuming you have the speed quints your starting MS should be 334. A single level of Raise Morale will speed you up to 344 and zeal will hit you at 370 as fast as most characters with boots. When you upgrade to Phantom Dancer adding another additional 7% MS with a second level in Raise Moral you are hitting 395. Activating that will move you up to 435. You basically have a low CD Ghost at this point.
Now you need to start adapting. Getting another Zeal to help chase and improve crits if you are doing well. Sheen if you are having mana troubles. Phage if you are dying. Then finish these into Trinity Force. Afterwards you are going to want to build Infinity Edge then another Phantom Dancer to get your crits to 100%. Somewhere you are going to want to grab Bloodthirster to improve damage and let you stay out longer. Your lifesteal will proc on Parrrley btw, so at this point you've got a nuke that does anywhere from 300-700 damage and heals you for 15-25% of that with about 5 sec CD.

The last item depends on what is going on in the game. If they are stacking armor Last Whisper, Madred's Bloodrazor or Black Cleaver. If you are chasing a lot Frozen Mallet works great and adds some survivability. If you need some MR you can grab Hexdrinker or even Force of Nature

This last item is the fail safe. Also if you need it earlier get it! Staying alive is more important than ganks most the time. So if you need to grab one of these earlier do so.

Basically max parley ASAP then raise moral then remove scurvy with cannon barrage when ever you can. I like to take at least one point in remove scurvy for the cleanse early.

You are a harrasser! Start out using parley you harass any squishes in lane as well as for farming. Hit up your E if you need the damaged boost for team fights or to harass a big harder. You should have much in the way of mana problems unless you go crazy.
Mid game coordinated for ganks you should be able to keep your lane at around half health so banking shouldn't be tough shot an ult that forces your target to run through 3/4ths of it or head towards you then eat their face with E then Q and the AA and Q when you can.
Late game you wanna wait till the team fights have gotten going then blaze in to take out carries with the E Q AA Q combo at this point you should have 100% crit chance and nd dealing massive damage. You will probably die but you should take out a carry and at least seriously wound a couple others.

Gangplank works amazingly well with support champions. Some obvious winners are kayle, nunu and sona: all of whom have some form of cc a heal and speed increase, sona's hymn of valor and nunu's blood boil also are amazing spells with him.

Again I will emphasize map awareness. If you need to spend your ult to let a running teammate escape do it cause it's worth it. If you know they are about to initiate a Hank lay it behind the enemy to give your teammates some zone control. Peoples first instinct is to avoid the giant ring of cannony pain and most don't have the presence of mind to coolly decide to take that damage and survive. Several times I've seen enemies engage 2v1 or 3v2 because the weren't going to retreat through the cannon field, even when it would mean they would live.

Also a word of warning: don't be a ****. You should be getting lots of kills and it will look like you are KSing at times, be a man and apologize if that happens. It's a little thing that will keep your team running smoothly.

Kick butts and take names and let me know in comments if youve got suggestions.