Links to websites of companies, accommodation etc that I've found to be particularly good or useful.
Casa Maricela y Gilbe - a really good Casa Particulaire in Vinales with great food and helpful hosts
Sepilok Forest Edge - good accommodation in Sepilok and handy for the Rainforest Discovery Centre and the Oranutang Rehab Centre
Mantanani Backpackers Lodge - the only way to stay on Mantanani Island for Phillipine Megapode and Mantanani Scops Owl
MASWings - the place to book cheap internal flights within Sabah
Quetzal by Car - really good site for general info and planning
La Selva Biological Station - booking for La Selva
Savegre Natural Reserve and Spa - birding heaven!
Costa Rica Gateway - a gateway to many sites
Chiang Dao Nest - great accommodation at top birding site
Thai Birding - great website for trip planning
Birding2Asia - GPS co-ordinates for North Thailand birding sites
Explore Georgia - good company to arrange transport from Tbilisi to Kazbegi
Hotel Rooms Kazbegi - the best hotel in Kazbegi
Birding Gambia - 'zoomable' map of the best birding sites
India - Goa
Backwoods Camp - prime birding location/accommodation/guided birding - a must do!
The Hermitage Guesthouse - small eco guesthouse in great birding spot in the Western Ghats with wonderful food
Arinza Towers Hotel - reasonably priced accommodation in Kuwait City where most places are expensive