Yahoo has just started offering Sponsored Listings for between $25 to $300 a month, depending on category. 5 sponsored listings are displayed at the top of category pages (if more than 5 people buy sponsored listings, they rotate randomly). In order to get a sponsored listing, you must first get a normal listing in Yahoo, then you can apply for a sponsored listing in the category your listing is in. You can't use this to change your listing title or description, by the way; it just gets you "up top."
Is it worth it? My experience is that Yahoo Sponsored Listings totally suck! Not only are the clickthroughs dismal, but when I applied for a sponsored listing, Yahoo edited my current Yahoo listing and totally trashed it. Talk about adding insult to injury! Even worse, I have been trying to get a response from Yahoo on this, and so far, they haven't responded, even to my requests to cancel my sponsored listing.
Yahoo has also introduced "Most Popular" listings underneath the sponsored listings; so far it is unclear how a site becomes a Most Popular site.
Update: On December 28th, 2001, Yahoo started charging $299 a year for new listings. Old listings are grandfathered. No package of money has arrived for me yet, but I live in hope.