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! Yahoo was totally unresponsive to my inquiries regarding this action.
Note: Please don't confuse Yahoo's Sponsored Listings that appear in the directory listings with the Overture Sponsored Links that can appear in Yahoo search results. The latter can work just fine, and I have written a tutorial on how to use them properly.
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.