Rich Ads in Search - Yahoo! says their initial tests have improved click-through rates as much as 25%. This month, they'll expand rich ads in search to large brand advertisers. If you do get access, it's ultimately the conversion rate that matters the most, so keep that in mind.
Ad Delivery Report - Launched last month, the report allows you to see which ads appear on partner sites. It also allows you to block sites that aren't converting well for you.
New Web Search - Just a couple of weeks ago, Yahoo! rolled out their new search. The biggest change was the UI, which featured a new 3 column look.
Network Distribution - Coming next year will allow you to separate bids for Yahoo! and partner channels.
Yahoo! Search Marketing Desktop - Also coming next year, this will allow you to manage search ad campaigns offline. The tool is currently in beta and if you're interested in testing it, you can sign up here.