The best thing for cleaning parts is regular old solvent, but they don't sell it at Wall-Mart; it's more of an industrial supply type thing and I think it costs around $10/gallon. For engine cleaning, I've found that Gunk engine degreaser works best unless things are really messy. I actually just used some yesterday on my Grandpa's Lumina (it's going to need some gaskets and a coolant flush), which was dirty but not terrible, and it took it right down. I think the Gunk degreaser is about $1.50 at Wally world, so it's not too pricey (their store brand "Super-Tech" stuff at something like 80 cents, by the way, is next to worthless in my experience). Basically, while gas and diesel can be used as a solvent, it's not a good idea in general. We all know that gas and diesel are fire hazards, with diesel being less of one, but breathing the fumes of either for extended periods is not recommended either. Of course you want to limit skin contact with any and all petrolium distilates. So, I guess anything you use will probably kill you in the end. My dad keeps telling me should just give it up and be a gerdener, just dirt and water there. Ummm... that's ok.

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Once and future king:
'64 Ford Fairlane w/approx 238,000 - looks rough, but amazingly reliable if you know how to look after it; I will soon begin work to totally restore and modernize it.
Family vehicles that I lay some claim to:
'78 300D w/approx 350,000 original, '62 Ford F100 4x4, '90 Ford E150 w/171,000 original