For mild stuff, isopropyl alcohol will clean much of it off. Most circuit boards will withstand soap-and-water cleansing--be sure to dry them.
Beyond that, it depends. I've cleaned a half-inch of mouse feces and urine off of circuit boards using oven cleaner after nothing else would touch it. Worked just fine, but the board had no aluminum parts on it.
On metal, if things are really greasy and a mild cleaner such as Windex doesn't touch it, mineral spirits will generally get stuff off.