I really enjoy having History Hound at hand. I end up using it a dozen times a week just to find some page I hit but didn't bookmark. The tool integrates so well with my workflow that I don't even think about it until right when I need it, which is perfect.

With the flexible indexing I have History Hound can search archives of NetNewsWire, and even your own webpages, etc (if you're a web developer, this can be nice for finding a snippet you put into a site, etc).