This isn't meant to be a comprehensive guide like Batesii's... I just wanted to show you guys an interesting build I've worked out that really rocks. The cooldown reduction is key if you use the right playing style.... You might not be the one landing all the kills (you don't want to tower dive with this build), but you'll be carrying the team by doing a ton of damage in little bursts, diving in and out constantly.
Getting PHAGE early on gives you the tankiness you need and it also lets you slow down anyone who thinks they can get away by using your Hyper Charge in Cannon Mode.
Attack speed is key with the black cleaver being a nice choice.

When you adjust the build to suit the current game, just make sure balance three factors: tankiness, damage (for the massive cannon shot), and MAGIC RESIST (very important because everyone will be targeting you constantly!!!) (That's why I use flash to get the hell out of dodge!)