Simple Green.
Cover your electronics (alternator, fuse box, bare connections), spray it down with water, drench with SG, use a wash mitt to lightly scrub, and rinse thoroughly.
To give the bay a shine, look into a product called CD2 Engine Detailer. When the engine is almost dry, spray everything, then run the engine for 15 minutes to "bake" it on. It's essentially an Armor All-like product for the engine bay.
You may have a little difficulty finding it, as either it was phased out (hope not) or its product highly cut back. But, it's worth its fluid weight in gold.