This is just a quick dump of links I can think of off the top of my head. I'll probably add more content if I get a lot of questions.
Wikipedia entry for GMRS contains a lot of information and links relevant to both FRS and GMRS radio services. FRS is license-free and has fewer rules but lower power than GMRS, even though both operate on the same frequency channels.
Midland Radio GMRS License Info has instructions for how to buy your GMRS license from the FCC, and some talking points about GMRS. Midland also makes some good, affordable GMRS radios, several of the mobile and micro-mobile units can use repeaters.
Wikipedia entry for CB Radio talks about the frequencies used and propagation characteristics. CB radio is a personal radio service that does not require a license.
HamStudy is one of several sites that offers information about amateur radio, including practice exams and other study materials to help you ace the exam.
ARRL Amateur Radio Bands Chart shows what frequencies can be used by licensed amateur radio operators of varying classes