I have been delighted with a Perl-based commercial solution that doesn't break the bank but that is more powerful than anything I've seen in the freeware/shareware area (and I think I've checked 'em all):

http://northernlight.com/engine.html

(the Northern Light Enterprise Search Engine).

I'm still configuring it, but it's running in a sort of beta state on my site at

http://benefitslink.com/search