Benin, Burkina Faso, Cameroon, Cape Verde, Central African Republic, Chad, Congo, Cote d’Ivoire (Ivory Coast), Equatorial Guinea, Gabon, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Mauritania, Niger, Nigeria, Sao Tome and Principe, Senegal, Sierra Leone, and Togo.
Nik Borrow and Ron Demey’s Birds of Western Africa (Princeton Field Guides) (ISBN 978-0-691-12321-9) covers all 1304 species recorded from 23 countries (listed above) in West Africa. It’s a good guide; it’s the one you should have for birding in the region.
It contains everything a field guide should: color plates, species descriptions, and range maps. Most species accounts contain disc and track numbers referencing Claude Chappuis’ African Bird Sounds CDs.
The plates are good overall but would benefit from arrows or notes indicating key field marks. While birding Cameroon with this guide, I found the range maps to be misleading in a few cases, which is probably because the region is not heavily birded and much remains to be learned — even from observers like you and me. There are special sections in the back illustrating birds endemic to the Cape Verde and Gulf of Guinea islands. The book does not contain any French names or information, which is too bad for Francophones living in Africa and visiting from overseas.
Birds of Western Africa is a condensation of A Guide to the Birds of Western Africa (ISBN 978-0-691-09520-2) by the same authors. It’s a large, heavy volume not suited to field use. It contains more extensive species accounts than the brief summaries in the smaller field guide. I don’t own a copy, but I had a chance to look through one, and it looks like it would be a helpful companion to the field guide if you want to spend the money. The plates are the same in both books, though a few newly recorded vagrants (like Great Blue Heron) are added to the more recently published field guide.
Birds of Western and Central Africa (Princeton Illustrated Checklists) (ISBN 978-0-691-00714-4) covers many of the same countries as Birds of Western Africa, but I was not impressed with it. The illustrations not very good, especially for species that are drab or otherwise confusing. It’s small and could be handy for carrying around in a pocket, but if you get stuck with a tough ID, it might not be much help.