In my experience of all the ones I have tried, 505 is the best basting spray:
http://www.amazon.com/Odif-Usa-10-93...dp/B0018N73C6/
However, there is a newer one out that I haven't tried that is supposed to be even better. That would be Thermo O Web Spray n Bond:
http://www.amazon.com/Therm-Spray-Qu.../dp/B007POWZGG
Note: Amazon doesn't necessarily have the best price on these. It just provides convenient links to the products.