IMO - Tanners Leather Oil is the best thing you can use.
It is cheap, it protects, and more importantly you would have to put an insane amount on the leather to damage it (over oiling can cause as much damage as under oiling)
http://cgi.ebay.com/Tanners-Leather-...QQcmdZViewItem
I ruined an expensive Corbin motorcycle seat by putting the popular products found in automotive stores on it (lexol / zymol / etc)
After talking in depth with a local leather shop owner, I discovered that using the tanners oil once or twice a month with a nice light coat was the way to go.