what do you guys use to clean your engine bay?

Simple green is the way to go. Put some in a spray bottle and mist everything down with it. Let it sit for a while, scrub, and rinse. Heavy grease spots might need a second application and scrub job, but they'll come clean.
 
Any degreaser. Dont buy that crappy engine degreaser in the spray can. Buy some actual degreaser like purple power, or simple green. you can even use that stuff on the actual paint in the bay. I wouldnt use it on the outside of the car, but it hasnt harmed my paint on the inside, and does one hell of a job. Get a sponge, a scrub, and some degreaser and with a hose you should be all set. You can use some tire shine on anything rubber to make everything black look real clean.
 
Any degreaser. Dont buy that crappy engine degreaser in the spray can. Buy some actual degreaser like purple power, or simple green. you can even use that stuff on the actual paint in the bay. I wouldnt use it on the outside of the car, but it hasnt harmed my paint on the inside, and does one hell of a job. Get a sponge, a scrub, and some degreaser and with a hose you should be all set. You can use some tire shine on anything rubber to make everything black look real clean.

careful with purple power it will stain any aluminum parts in the bay if left on for too long, and it will eat the paint of the engine bay