Indica or Sativa? Weed (Cannabis) Growing Guide:

Hopefully, that link helps you figure out what indicas and sativas are. Basically, indica is more of a sleepy-body type high and is good for pain relief. Usually these are your Purple and Kush varieties. Here's a nice lil list that's being compiled to show exactly which strains are which:

Complete List of Cannabis Strains(and a lil more info - Grasscity.com Forums