A.M.
I like the Sony one. Its has a "voive activated" option that is great so you don't hear that constant white noise. It only makes sound when baby makes sound. There are no weird beeps and the range is very very good(we have a 2 story).
I used a few other brands that I received from baby showers and from family(even expensive ones) and I didn't like any as much as this one. I bought it as a recommendation from one of the mom's on this site and I'm so glad I did.
http://www.toysrus.com/product/index.jsp?productId=2815277