A former co-worker forwarded me a link to this application, HistoryHound. What a brilliant piece of software. It's one of those "It's so simple, why didn't I think of it?" kind of applications that I am sure I will be using a lot. It allows you to search your browser history by content. And it can keeps an index of any long size, independently of your browser's history.
I just bought a $20 license to the program. You should too, if you're a Mac user. You'll like it!