Best (most anonymous) method is to set up a load of proxys of your own... without logging enabled, on as many computers as you can... set each one to point to the next, then the final one into the internet
then from wherever you are, you just conect to the first in the chain...

if they don't have logs, its not so easy to trace, try to set them up on public computers (libraries, colleges, universities etc... preferably places with broadband net connections - they're always on... someone's home comp. with a 56k modem ain't a good idea!)

However, if you want to know this to try to hack something - give up now

Thay can, and will, find a way to trace you!