I recently found the Slogger extension for Mozilla Firefox; it's like a super charged version of the default browser history.
It saves every page you visit to a hard drive folder you specify, including all associated media and images on the page, like the "Save Page As" option in file> menu.

What I like about it is you can set it to save each page automatically and just forget about it, leaving it to quietly save everything until you need something.
It can be configured to only save the text of the pages to save disk space, or you can disable auto save and just click a button on the toolbar to save individual pages.

A good desktop indexing program would work nicely with this to make the history searchable - request to blinkx, please let me configure which file types to index.

A similar history enhancing tool (with built in search) is available for Internet Explorer, the Recall Toolbar, or if you like the advantage of having your saved pages archived online, check out Furl.net.

More info:
· Slogger homepage
· Slogger help pages