Boiling hot water with a good citrus cleaner is a good environmentally safe method. Soak them in the hot water for a while and then scrub them with a toothbrush to get the old grease out. It usually takes a few attempts to get them clean. Scrubbing with gasoline is the old standby if you have a way to dispose of it.
I,m a kerosene guy, seems to work quickest on real old crap. I have used brake cleaner and it is super quick and powerful but really dangerous to the body. I use it sparingly and as a last resort. But when time is an issue I will carefully use it. And yes I use kerosene because I do have a place to dispose. The brake cleaner evaporates on its own but I assume at a cost to the environment.
I had thought about using mineral spirits just because i have some on hand, but I'm thinking I'll try the alcohol or one of the hot water methods.
I agree with Matti on the Simple Green. That stuff smells great!