I use a system from wilife (
http://www.wilife.com/) who was recently purchased by Logitech.
It is a pretty good system - The starter kit includes the software and one camera and costs $250. Additional cameras are about $200. The system can handle up to six cameras and must be connected to a computer.
They have Indoor, Outdoor, and Spy cameras (embedded in clocks, etc).
I have two cameras, both Indoor models attached with suction cups looking outside.
It is a great system for having about $400 invested.
I already caught one neighborhood thief - broke into a neighbor's car and peeked through the windows of both of my cars.