Not Updated For Current Season
This guide isn't as much of an indepth guide as it is a guide about other uses for champs that people tend to overlook, but can be pretty effective or just fun to play. I'm also willing to look into other unusual builds to see if it can be done.
Tristana - AP Assasin
This is got to be my favorite build of all the listed. This is just extrmeley effective and really fun. Rocket Jump becomes GOOMBA STOMP and you hop around while it's cooldown is reset whenever you get a kill or assist. Your ult will hit up to 1k damage. Late game, Rocket Jump > Explosive Shot > Buster Shot usually always means a dead carry, with the plus of a healing debuff. You can also Rocket Jump right into a tower for a final blow and hop right back out. Also, you will damage towers for 40% of your AP when it surpasses your AD, you can knock down towers pretty quickly with Rapid Fire.
Master Yi - AP Burst Caster
Also one that I am well aquainted with, Alpha Strike does great damage and your more of a hybrid since about half your damage will come from Lich Bane. Alpha Strike is also great to farm like crazy, and Meditate can make you invinceable if you don't get cc'ed. If you want an indepth guide, I have made one you can view Here
Miss Fortune - AP Caster
This is a pretty decent build, and is great for team fighting. You won't be able to 1v1 very well, but with Make It Rain and Bullet Time, team fights will be over pretty fast. You can do single target damage becuase of Impure Shots.
Oriana - AS Carry
This build lets you do some pretty good damage, and you can just use your ball for support. You level up Command: Protect first because you won't have much AP so your looking more for the Utility from your spells rather than the damage.
Galio - AP Caster
This is a pretty high damage build, but is a little hard to play. Your damage skills are skill shots, but you will have alot of cc and AoE damage. If you want damage early, go with the skill order llisted, but if you want to be a little more support, get a level or two of Bulwark. When you ult the other team, make sure to Bulwark yourself so you can heal from it. If you really want to have some fun times, get an Nunu and a Maokai, buld them AP also, and you know where im going with this. Maybe throw in a Kennen to just for sh*ts and giggles.
I'm just the type of guy who likes builds that are unusual and fun. If you have a suggestion or something I missed, feel free to suggest it. If you have a guide for any of these builds, I'll link it if I like it and you allow me to. And remember, make sure you have fun when you play.