FRS Radios
FRS Radios are pretty easy to find, many places sell one brand or another, I've found that Motorola are usually the best to go with, plus they have plenty of models to choose from. Be sure to get one with sub channels; the sub channels don't hide your communications from others but the do block out all traffic from anything other than your sub channel.
Sometime in the Future I plan on adding a permanent FRS system that has better range and reception and doesn't need batteries (runs off car battery), but so far I haven't seen any models I like.