Check out this website http://www.smokersguide.com/sg/index.html it lists descriptions of over 200 strains. You'll see most are actually indica/sativa crosses.

The best way to tell if you've gotten an indica or a sativa is to smoke it. A saticva will make you happy, give you the giggles and munchies, and make you want to go and do something. Sativas are good if you're going out to a party or doing something active

An indica, however, will tend to give you a more relaxed, body high. A lot of medical users like indicas because the body high is better for pain. You're more likley to want to just kick back on the couch and watch tv. Maybe take a nap after a while.