The one piece of advice I will give you when choosing how much to put in as a cleanup crew is add slowly and diversity. I had alot more cleanup crew and ended up pulling out some to give to other people because they just were not needed. If i see a problem in the tank, I will add as needed. (IMHO - better than adding a ton then having stuff die off)
Below is what I currently have in my tank. I do have bubble algea that i'm fighting, my emeralds are stupid and don't touch the stuff so still working on finding something for that. (may keep catching them and trading them in till i get lucky) Other than that I don't have any visible nusance algea.
16 Gallon Nuvo - My cleanup/invert crew
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2 Emerald Crabs
1 Nassarius snail
3 Banded Trochus Snail - these guys are amazing
3 Adult Nerites - these suckers breed I have tons of egg sacks from them and at night all the babies are all over the place - or they could be collonista snails
1 Blue Leg hermit crab - some people don't like hermits because they go after the snails / my sexy shrimp are more of a pain than anything he does. (plus how much trouble can 1 hermit crab get into)
I don't know if people consider these part of cleanup crew or not, but will list.
3 Sexy shrimp (I consider them part of the cleanup crew since they are always picking at stuff)
2 Pom Pom Crabs
1 Porclain Crab
Hitchhikers
http://www.worldwidereefers.com/forums/showthread.php?4768-Hitchhiker-id-guide
stomatella snails (not sure if you can find someplace that sells them) probably have 3+
Spaghetti/hair worms
Bristle worms
spionid worms
spirorbid worms
vermitid snails
mini feather dusters
Notes about experiences in my tank w/ cleanup crew:
Hitchhikers are not technically purchased as part of the cleanup crew, but I count them...i think the fact that I have so many different types of hitchhikers taking the food/detris the below snails are not finding enough to eat and dying off.
Cerith snails - I hear really good things about them, but I keep getting them and they just die.
Nassarius snails - Same thing as the Cerith, they just dont make it. The 1 I have currently is a little guy and he seems to do fine, but larger ones don't make it long.
PS: it is not the hermit crab killing them he is innocent (i didn't get the hermit till after i gave up on getting more nassarius/ceriths)
I have thought about getting a bumble bee snail if I ever notice that I have way to many worms. (The reading is that they will go after worms so maybe to control the bristle worm population)
http://www.liveaquaria.com/product/prod_display.cfm?c=497+526+565&pcatid=565
anyone have experience w/ the bumble bee snail?
Also, I do wish I had something stirring up my sandbed better besides worms, but right now my sand bed holds most of my corals so that would just be a pain, maybe once corals glued down to rocks and off the plugs I'll look into something that will stir the sandbed better for me. (I just make sure to stir the sandbed every week when I do my water change.) FYI - sandbed is around 1" or less in my tank.