Indicas will give you a heavy, body stone. These are great for relaxing but are likley to lead to couch lock so you don't neccessarily want them if you've got stuff to do.

Sativas will generally have more of an up, head high. You can smoke them, get really high, and then go about doing whatever you need to do.

There are hundreds of strains out there, some are pure indica, some pure sativa, and some are a mixture of both.

Check out http://www.smokersguide.com/sg/index.html they've got tons of reviews of different strains.