What kind of rear wheel do I need? Recently my bike rear wheel was hit by a car at a traffic light. Now it's bent a little and touches the brake. It cannot be fixed by adjusting the spokes and I am going to need a new one. My bike is Schwinn varsity 1200. Here are pics of the wheel.
Look carefully at the tire, there should be markings on it that indicate what size wheel it is - generally 700 is a road-bike standard. 26 inch is a mountain-bike standard.

This is a good resource.

http://www.sheldonbrown.com/wheels.html

Also an option is the number of spokes, the more there are, the stronger and more abuse resistant the wheel is generally. Also consider do you have Shimano or another drivetrain- there can be compatibility issues.