Most plecos are non-schooling and some do not tolerate others of their own kind.
Some of the smaller ones are the gibbiceps or the bristlenose. That is only 2 of many. I suggest going to www.planetcatfish.com and check out all the plecos.
I do not suggest you get one for algae control as there are other fish that are smaller and more community friendly. If you want one to have a pleco is one thing but for tank maintenance is not a wise move.
You will need to check on compatibility with existing tank residents. To recommend one without knowing what you have in your tank is asking for problems.
Some grow to 4-6" and some get around 20" or more. Needless to say, they are not all equal in temperment, diet, or size.
Don't forget that also the small Otocinclus also eats algae, biofilm,etc and sticks to the glass as does the Chinese Algae Eater. The otocinclus (Otto) stays very small (1.75-2.5") and is a good community fish. The CAE isn't very friendly and when larger tries to eat the slime-coat off fish in the tank with him. Can get to 6". I don't recommend the CAE unless you have fast moving fish.