Port of the GPGServices to Snow Leopard.
See http://www.far-blue.co.uk/projects/gpgservices.html for details.

To compile and test (takes some time since MacGPGME gets compiled too):

git clone --recursive git@github.com:GPGTools/GPGServices.git
cd GPGServices
make
# now logout and login again
# then have a look at System Preferences > Keyboard > Keyboard Shortcuts > Services > Text > Import Key ..."