The GeoLite Country database at:

http://www.maxmind.com/app/geolitecountry)

is just fine for countries. The Ruby gem works nicely:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/...

... and there are other APIs as well:

http://www.maxmind.com/app/api

MaxMind is the standard.