hey im thinking of getting some snails for my smaller tank and then using them if they over breed to feed my large cichlid and loach tank but i have plants in my large tank so is there any snails that dont eat plants cheers 
Apple Snails - Lay eggs above water line so easy to remove and avoid hatching so avoid getting over run. Get the species Pomacea bridgesii as these wont eat your plant.
Nerite snails - I'm not sure if these guys actually can breed in freshwater...and even if they can they aren't prolific breeders and sell for a decent price.
Ramshorn Snails - Extremely prolific breeders, lovely intense red colour in the red versions, but only get them if you really have plenty of fish to feed them too.
Malaysian Trumpet Snails - Live bearing snails I think, some people have seriously problems with them. I've had them for two months and not yet noticed any explosion in population size... I think it is alot down to how much to feed. MTS live in the substrate (sand being best) and are the only true freshwater detritivores, you often only see them at night.
Assassin snails - When other populations get too high you can always try to control them with assassin snails.
Everything is safe with plants unless otherwise stated (hence telling you which species of apple snail)
If you google applesnail.net you will find everything you could ever need to know about them, including how to distinguish different species from one another.