We enjoyed Oaxaca very much. If you've made it this far, you may interested in visiting, too. To help you, we've assembled resources we found very helpful.
There are many general guides to Mexico, and even several on Oaxaca. But for us Lonely Planet's Mexico, Lonely Planet (2002) was the most useful. Its opinions on restaurants, shops, hotels and shopping were accurate.
Howell, Steven N. G. an Webb, Sophie, A Guide to the Birds of Mexico and Northern Central America, Oxford Press; (May 1995). The definitive guide to Mexican birds. Big, thorough and heavy, it covers almost every documented Mexican species.
Peterson, Roger Tory, A Field Guide to Mexican Birds : Mexico, Guatemala, Belize, El Salvador, Houghton Mifflin Co; (March 1, 1999). Not as exhaustive as Howell but much more portable.
Forcey, John M., Birds & Birding in Central Oaxaca, Impresos Arbol de Vida, Apdo 6-17, Oaxaca C.P., 68020 Oaxaca, Mexico (1998). John Forcey is the dean of Oaxaca birding; this pamphlet is the definitive guide to the Valles Centrale.
Not everyone needs or wants a guide. But a good guide knows the hot spots, knows where the birds are and knows the birds.
Roque Antonio Santiago ("row-kay") is very good on the Valle Centrale and mountain locations and birds, and good on the Gulf Coast locations. Strongly recommended. A.V. Juarez #59, Teotitlan del Valle, Oaxaca 70420 (firstname.lastname@example.org). Pay attention to what Roque recommends on local artisans, too.
John M. Forcey is the author of a nice birding guide to the central valley of Oaxaca and sometimes guides. Apartado 1415, Oaxaca, Oaxaca 68000 (email@example.com)
Ramiro A. Perez may not be available to guide; he has research projects under way. But he is a knowledgable, experienced birder and a very nice guy (firstname.lastname@example.org)
The Pacific Coastal birding is terrific, but getting there is an ordeal. The buses are safe and reliable, but you may want to fly at least one way, especially if your time is limited. Check out Aerotucan, which flies daily between Puerto Escondido and Oaxaca City.
In Oaxaca City, the Hotel Victoria has a reputation as the finest hotel in the city. We didn't stay anywhere else, but we can attest the the Victoria is very nice, on well-maintained grounds on a hillside above the city. It's older, but well-maintained, with a friendly staff and a nice restaurant.
Talk to your credit card company before you leave. Tell them you are going to Mexico. Obtain approval for transactions to some fixed amount before you go. Otherwise, your credit card company, in its zeal to prevent improper charges, may block your card entirely, as happened to me. Take two cards from different banks, too; same reason.
http://oaxaca-travel.com Oaxaca in the Heart of Mexico - general information about Oaxaca City and State.
http://www.oaxacatimes.com/ Oaxaca Times.com - general information about Oaxaca City and State; some feature articles.
http://oaxacalive.com/ Oaxaca Live - general information about Oaxaca City and State.
http://www.fatbirder.com/links_geo/america_north/mexico_oaxaca.html - Fat Birder's general information and links about birding in Oaxaca. Slightly dated but still useful.
http://www.wincom.net/~pelewing/hvecotur.html - Hidden Voyages Ecotours - Michael Malone's well-regarded tours of the mangrove swamps of the Pacific shore. It's probably important to make certain the Malone or his wife, J. Walker, is you guide.