I’m sure many of you have heard of this before, but I was just reminded of it recently. Martin Aignesberger has written a bunch of utilities, one of them being software that checks your bookmarks:
AM-DeadLink detects dead links and duplicates in your Browser Bookmarks. If a Bookmark has become unavailable you can delete it from your Browser. AM-DeadLink checks Bookmarks from Internet Explorer, Opera, Mozilla and Netscape.
I just ran it and I have 276 bookmarks, and 18 of them are bad. Of course I probably haven’t visited over 200 of them in last year, but that is a different problem entirely.
Check it out at http://www.aignes.com/deadlink.htm