I use the (free) SBL and XBL blacklist service from Spamhaus and it is really, really good. In the first ten days of 2004 it blocked over 2,500 emails from our server. I also use www.blackholes.us (blocking China, Korea, Brazil, Argentina and Russia). That is also very effective - it blocked nearly a thousand in that period, yet it still let in an email from Hong Kong.

Gareth