Don't use wireless if you can help it.
My neighbor put up wireless on the same channel as my remote controlled car, so now his living room gets recorded on one of my DVR channels.
I put up a sign with Mr. T saying "Don't be a fool and use wireless cameras" then turned on my 200mw transmitter so they would know they were being watched.
Have you heard of war driving where people go around looking for 2.4ghz networks? People can do the same thing with a wireless video reciever in their car and drive around looking for people who have cameras. They can case your house from the inside, if you have audio they can learn a lot about you too.
Maybe you think your camera does not transmit very far, but I use a 13db high gain omni-directional antennea and they are like $40. I can see a long ways and don't even know where my neighbor is... could be a block or two away...
If you have thought this out and are cool with the risks, here is some advice. Get a camera with WEAK transmittion and get a good reciever. When I drive my RC car, people for a mile can probably see its video. So transmit less and receive more.
I also recommend an 8 channel PLL reciever/transmitter like www.blackwidowav.com and use one of the higher channels so people with cheap 4 channel receivers can't see your transmittion. I bought my gear from www.microcameras.com because I don't like BWAV's site & business practices.
Avoid all of X10's crap. Just get a little Swann/SecurityMan/Q-See setup if you wanna stay on the cheap side. Sometime's Geek.com has some wireless night vision 2.4g cameras for $45. I have one and it is decent for CMOS/the price. and it is outdoor/weather proof, it also has an RCA in case you decide to use it wired...