Tools for monitoring email

A number of groups provide tools for monitoring email performance.
Some of these tools are provided by ISPs, like Hotmail and AOL have postmaster webpages. Hotmail also provides things like SNDS so you can monitor what Hotmail is seeing about your network.
Al has a new blacklist stats center over at DNSBL.com. Of interest is the accuracy of some of the widely used lists like Spamhaus, Spamcop, and PSBL. Other lists like FiveTen were wildly inaccurate. In fact, Al has shown that blocking mail from any IP with a 7 in it is more accurate (more spam hits, less non-spam hits) than FiveTen.
ReturnPath provides free reputation lookup and monitoring based on the data they acquire.