The radio in the 4.2 RAV4 is a bit wider than 2DIN, the depths is a bit limited though. In general, all 2DIN LCD units should fit, the installer just needs to put a bit of framing around it, and if the unit is too deep, then it may stick out a bit. I have the Eclipse AVN2454 all-in-one (NAV+DVD/CD+radio) in my RAV4, and i think it fits pretty well, although it sticks out a little bit more than i initially expected. Looks like this:
More chatter about that model in this thread:
http://rav4world.com/forums/viewtopic.php?t=15
If you do not want navigation then there is quite a wide range of options from Eclipse (
www.eclipse-web.com), Kennwood and Alpine. Not sure if Pioneer also has 2DIN LCD systems (not fold out). If you want to be more adventerous, check out drivesoft.net or other PC-in-a-car manufacturers. Not sure if they have 2DIN size displays on offer though.
Beside the mechanical, the only electrical issue is that you will need something like the infrared SWIX for the steering wheel audio buttons. I do not think there is any third party radio that can be wired to the steering wheel buttons.