Jonathan Christopher has released a commercial plugin called SearchWP. The plugin aims to improve WordPress search, and put control into site administrators hands to tailor results. It looks pretty nice, though I haven't used it yet. It's available for $25 per year for one site, or $250 per year for up to twenty sites.
SearchWP is the latest option for improving WordPress search, which is a good thing, because WordPress search stinks. Other options I know many folks have used are Swiftype, Relevanssi or Google custom search. I look forward to checking out SearchWP a bit further.