SORBS is one I know. It doesn't do any filtering in its own right, it just provides its database to subscribers. I've had stuff "blocked" by it: it's probably the most aggressive of the bunch.
However, to get yourself listed on SORBS, there must have been something to cause that - Spam, or an open relay, or who knows what.
When it happened to me, my ISP found that the cause was ONE subscriber on the ISP who had done something silly (but quite a lot of it). It was sorted and the problem went away.
I'd start with your ISP. In theory, they should care!