Compactor / Obfuscator

I would like to find a good JavaScript compactor/obfuscator.
Obfuscation is not important to me really, but I would like a
compactor that understands variables and functions in a way that it
can shorten the names. I would also like for the compactor to be able
to shorton the property/method names of custom objects if such a thing
exists.

I have seen several compactors around, but most of them have varying
levels of compression that don't seem to be very customisable. Again,
obfuscation is not a must, although any good compactor should
obfuscate the code within reason anyway. If anyone uses GMail, and has
seen the code, that serves as a good guide to what I'd like to see
happen with my code.