Nick has summed it up very well....You need to decide if you want DLP or LCD technology. If you want a projector that is capable of 720 or above HD material, the LCD route will be more affordable. To get a 720 DLP projector will be much more costly. Also, I recommend you try to demo some different units before you buy. Many people suffer from "the rainbow" affect when using DLP projectors. Basically this will look like a fluttering of colors during certain scenes. If you suffer from this, you will not enjoy your projector, or if a spouse, child, or friends suffer, they won't like it....
I love my Sanyo Z2, and am looking at the Z3 like Nick possibly.
A good starting point 
