Came across a couple of neat domain lookup tools this week. The first is a Firefox extension which looks okay, but doesn't include Tucows OpenSRS or IYD in its list of registrars.
Domain Lookup Firefox Extension: "Domain Lookup is a Firefox extension that helps you discover valuable generic domain names while surfing the web."

DLF mentions lookup privacy in passing - I'd be really cautious in any event. Domain Name Frontrunning is real and could cost you valuable domain names.

The other tool comes via Jon Lax - Domize, a fairly nifty little web-based look up tool allows you to search for your favorite domain name in real-time via a configurable list of default registrars. The list of registrars is fairly small, and I found their UI a bit confusing, but the realtime search was pretty useful. Domize doesn't really say a lot about lookup privacy - until I learn more about who they are and whether or not they absolutely guarantee that they won't use the search input for anything but whois lookups, I'll probably be steering clear.