You can obtain a list based off of the 1990 Sibley/Monroe world list
and the 1993 supplement at:
http://www.ornitaxa.com/SM/SMOrg/sibley4.html

It is up to date as of February 17, 1998. According to that list
there are 9702 species. However an updated list recent as of January
1, 2003 is available at:
http://www.ornitaxa.com/SM/TaxChanges.html

According to that list there are 10097 birds in the world.

It should be mentioned that the list includes extinct species and it
has been stated in other comments that counts like this are always in
flux and a matter of opinion.

This brings up an interesting question that I have had for a while.
Is there any "official" site or sites that distribute the various
lists? I found the above site because it was the first hit on google.
I doubt that it is the definitive source and it seems that everyone
keeps their own copies based from various sources. It seems logical
that organizations that complied the lists would distribute them in
some form or another.

Aaron Martin
mailto: aamartin at gmail.com