While I have my engines out I'd like to clean the engine bay, whats recommended to use and what should not be used?

I don't want to remove all the pumps and other items, but would just like to try to remove some stains etc.

For a general cleaning I would start with Simple Green.

For stains, like in the bottom of the pic, I sprinkle down Oxyclean and then hit it with bleach. Rinse thouroughly. Not sure why I have a "before" pic and not an after!!

Yes, simple green works well.

I use purple power. Seems to work very well for me and it is way cheaper than simple green.