StickyHydro,
You have a number of options here. Firstoff, there is the good old Gunk Foaming Engine cleaner. You spray it on a warmish engine, wait and then hose off...heh, preferably at a car wash. If you're going to use a high pressure hose, just stay away from the electrical bits.
If the engine is out of the car, I've used kerosene with great results.
One thing to keep in mind. A number of engine cleaners tout the fact that they are "environmentally friendly". That's all good and nice, but the crap that you're cleaning off your engine isn't. Just be aware that dilution is the solution to pollution.
Bogatyr