The Intellect Devourer is a lot of fun...

Otherwise this link might set you in the right direction. Keep in mind your character will have the (su) abilities of the new form.

Another creative use is to share the metamorphasis with your psicrystal. Astral Construct is a versatile form. One you are of sufficient level, I am sure you can think of nasty things to do with the various types of Golems.