Adventour - great source (with beautiful pictures) for trekking, skiing and exploring both Central Asia and the Caucasus. Warning: this site will make you want to leave immediately.
Caravanistan – good resource. Includes a travel agent database with tours of Central Asia, an expanding guide to accomodations, and an ‘essentials‘ section with information about visas, border crossings, maps and travel guides.
Somon Travel (disclaimer: We have not used their services, but they specialize in CA and their website offers information about travel and visa procurement) This site is also good for ideas of what to do in the CA republics.
Sokol Tours – another specialized company, again, no prior experience however it offers information about travel in the region
Community Based Tourism (Kyrgyzstan-specific) – highly recommended!
State Department Travel Pages: