30 weight oil mixed 50/50 with mineral spirits. About 5 bucks a quart, which will last about 20 years.

Last night after cleaning the chain I did throw on some Boeshield, because I couldn't find the oil bottle. I bought the Boeshield because people said it was awesome - but I found it not really any better than just regular old oil. Same with about a half dozen other bike specific lubes that I've tried.

The nice thing about spray lubes is that they're fast - you can lube a chain in about 5 seconds. Boeshield is extremely expensive though. If I want to use spray lube (like in the winter when I just don't want to be in the garage lubing a chain when it's -10*F) I use DuPont Teflon+Wax spray, $5 for a big spray can at Lowes.