I use Lock Ease- it looks like this:http://www.amazon.com/Lock-Ease-Graphite-Lock-Fluid-3-4/dp/B0006MWPZA
It is graphite in a liquid vehicle, and the liquid evaporates fairly quickly. A drop or two applied to the key and the key inserted into the lock should be enough. By the way, wipe the key off 'cause you won't want to get graphite on your clothes (or anything from your gashole for that matter).
Brian
(Insert smart comment here)
What are you guys doing to keep your gashole key lubed. Mine is getting so I unlock the gas cap and the key stays turned! I have 30,000+ miles and never lubed it.