To help a service get unlisted by a spam block list, try the following addresses for each blocking service:

To get in touch with many major ISPs, these links are of help:

ISP Postmaster Feedback loop Whitelist
AOL Postmaster FBL Whitelist
Comcast Postmaster FBL
Hotmail / MSN Postmaster FBL

I will add to this list as I find more resources that I’m actually using for delisting. Another good source for information on feedback loops is Word to the Wise.