A ton of different ones, not so much variation in the bodies like in the fish world, but in coloration, anything blue, green, red, red/ white, white, clear, orange ....TONS
Here's a good site that has some on them with pictures Blue Pearl Shrimp
Also if you're interested in keeping different once, make sure to check here which you can house together and which you can't Dwarf Shrimp Compatibility Chart - Freshwater Shrimp - TheShrimpFarm.com
Personally I use 10g's to be set up for shrimp only. For one I do this cause many fish will regard them as food, so not only do you get rid of your shrimp, but also you don't have no babies that way. Second reason, the very first shrimp I had with some Guppy way back when I then moved to a 10g alone and the change in the behavior made me have shrimp-only tanks after that. They get so active if no predators are around and I find it bunch fun to watch them. Specially if you use some dark sand as substrate, so for one their colors look better and for two them lil guys working & sifting through the grain of the sand is fun to watch.
Depending on which exact shrimp you plan on getting, they grow anywhere's from 1-2" long.
For food I always use dried pumpkin, sperulina pills, or lil bottom feeder tab's; they will "clean" the ground for any left over flake food too. But just like fish are, a good diet makes a healthy & shiny colorful shrimp.
If you wanna house them with fish, offer them hiding places to not permanently stress them out. As far as how many, I usually start out with a gang of 10 shrimp per 10g tank and let nature do the rest from there.
My personal fav's are Red Cherry's and Crystal Red's. Often found in stores (here at least) are ghost shrimp.
Oh and when you do that, just as a hint/ friendly advise...Allow your existing tank to be WELL established first, they do not do well in newly set up tanks. They also don't appreciate tanks that get administered lots fert's and the Filter's is usually their death sentence, so either cover the intake up with a fineeee netting or place them ideally in a tank with a sponge filter (that's what I have, works great).
Hope this helps out for the moment