I did some research, and it really depends on whether or not you want a PTZ (Point Tilt Zoom) camera w/HD or not.
The really good ones are super expensive, but it depends on whether or not if you can live without a PTZ or HD.
I use the Foscam line of cameras.
I use 3 of the foscams. 1 for the side of the tank, 1 for the sump, and one more that points into the living room. If you decide on a foscam, you can sign up on their website for their newsletters and deals. They send out deals and discounts through that.