On my chains, I just use Pedros Extra Dry lube (about $6, last pretty long too)... Works well for me.

PS: Make sure you degrease your chain before adding new lube (esp. after not cleaning your drive train for too long

EDIT: I'm adding this re. motor oil: it attracts dust like crazy, so your drive train will be all greasy and black pretty soon, and you'll need to clean it more often. Defeats the purpose.