spamhaus are a fairly good black list provider
as is SORBS and SURBL
edit, - when i say that they are good I mean that tey are some of the largest, and they seem to (in my experience) block quite a few addresses,
however my experience is sadly based on the side that they've generated false positives,
as wmorri said, you could generate your own black list, however, you'll usually find that this just means that you spend the whole time playing catchup.