+1 on a block list sticky. I'd also like to see different sample blocklist sources for those of use hosting services vs those of us consuming services.
As a host (hosting lots of web sites, so for example all my WordPress sites are constantly scanned, and all http/ftp/ssh etc ports are under constant attack), this is what I'm using as an IPv4 block list:
https://isc.sans.edu/block.txt (DShield Top 20 bad guys)
http://feeds.dshield.org/top10-2.txt (DShield Port Scanners)
https://zeustracker.abuse.ch/blocklist.php?download=badips (ZeuS bad ips - not the most restrictive list but won't have false positives)
https://rules.emergingthreats.net/fwrules/emerging-Block-IPs.txt possibly overlaps the DShield lists? I don't host email so not sure if I need this.
http://cinsscore.com/list/ci-badguys.txt CIArmy active threats. This gets by far the most blocks.
This is by no means an endorsement of a proper hosting block list, though it does seem to block quite a bit of bad traffic. In fact, I'd appreciate any suggested changes for a hosting provider that wants to block the worst of the worst while avoiding false positives. Thanks!
EDIT: I found a very good resource of blocklists: http://iplists.firehol.org/ has several. For my use, their Level 3 block list seems to be exactly what I need.