Many birders are familiar with Nigel Wheatley's excellent "Where to Watch Birds In ...." series. This is another excellent regional guide to the countries of Asia excluding Russia (covered in his "Where to Watch Birds in Europe and Russia"). This is the book I would go to first when deciding which country/countries to visit and then pick up a more specific book for site guides to that area once this book has helped you make that decision.
A total of about 260 sites (national parks areas, reserves, etc.) are covered in the book for all of Asia. For example Malaysia has 15 sites including such famous places as the Danum Valley and Fraser's hill. The section on Danum Valley is three and a half pages long including a detailed trail map from the field centre. The account begins with a brief description of the Danum Valley dipterocarp forest. The endemic species of the area are listed next followed by a list of "specialities", birds that are more easily found here than in most other areas of Malaysia. A list of other species of interest follows with more descriptions of the birding trails, the canopy walkway, and hints on night birding (for Large Frogmouth). Directions to Danum and local accommodations are also included and the account ends on the page with an enticing black and white drawing of Blue-headed Pitta.
The only reason I rated this at 4 rather than 5 stars is the published date of 1996. It would be nice to have an updated version but as I mentioned use this to make some decisions on your trip then follow up with more specific local guides and updates to reserves and lodging on the net. This is still wonderful to have in hand to peruse the possibilities of birding Asia.