I just stumbled across http://www.dnsstuff.com, which is a handy site that gives you access to a bunch of functionality from one page:
Reverse DNS lookups are the best. I use the full version of NEOTRACE, but here is a link to free express version.
Cool. Bookmarked. I also like Netcraft's stuff. For some bizarre reason, our network admins were blocking download.microsoft.com (what?!?!?!) which was a problem when we needed to download a service pack. I used Netcraft (http://uptime.netcraft.com/up/graph/?host=download.microsoft.com) to get the IP, set up a host file entry for download.microsoft.com (only the dns was blocked, not the IP... ?!?!?), and downloaded the service pack. Anyhow, Netcraft's uptime graphs are cool, and it's fun to see who's running what.
Nice link KC, thanks! Maybe you'll find following link intresting too: http://www.dnsreport.com/
And of course, my personal favorite -
It has most of these tools plus a small virus report area to keep current on the bad guys!
www.checkdns.net is my favourite site for this stuff