I got a Logitech USB keyboard that they specifically branded for use with a PS3. As near as I can tell that just means it has a longer USB cable than they'd use on a regular computer keyboard. Its cable is 8 feet long, which is a comfortable TV to couch distance in a lot of living rooms.
here's the one I use:
http://www.amazon.com/gp/product/B000ODP9H2/

There's also the option of getting a USB extension cable if you want to use a computer keyboard whose only problem is that its cord is too short.