Walkie-Talkie info

If you like driving with friends, you will find that having radios makes these trips much more fun, and safer.

Radios really only work line of sight. Any FRS/GMRS radio will work. The Motorola ones seem to work best. They are simple to use and get the job done. Note that channels 1-7 and 15-22 can transmit at a higher power.
If you want something with slighy better range you can get a FM/UHF/VHF radio like a Baofeng UV-5R+.

They are more complicated to use and require programming to get the most out of them, which can be a bit of a hassle. See below for stuff that will help with that, and get a programming cable.

CHIRP: A desktop application to program your radio.  With this program you can open an existing file someone created, or make your own, connect the programming cable to your radio and computer, and upload the file to your radio.
Frequencies Free by Jaap Crezee: App that converts FRS/GMRS channels into MHz. Note that entering sub channels (x.1, x.2) requires a bit more radio programming.