
join the club! I've got a bunch of pond snails in one of my tanks, they are a pita.
What else do you have in the tank? A good dose of copper based meds or snail killer (aquarium, not the standard garden snail killer type) will wipe them out pretty well but don't use anything like that if you have other inverts (shrimp, etc) or sensitive fish in the tank (like scaleless fish such as eels). You might want to steer clear of this option if you ever want to keep saltwater inverts in the tank also.
Unfortunantly I have both shrimp and eels in the tank atm so this option is out for me
Another way that has worked well for me in the past but takes alot more time and effort (but less nuking with chemicals) is placing a cup in the tank with an algae disk overnight then manually removing any snails inside the cup. Replace the cup and the algae disk and repeat as often as neccessary. Be sure to squash any snail eggs you see as well to limit population growth.
Be warned though, short of pulling your tank apart completely and rinsing it as well as the substrate, decorations, etc with scolding water you will most likely always have at least a couple in the tank unless you are extra perceptive of the problem or use the first option.