Yahoo Mail is Yahoo's free, Web-based e-mail service. The newest release feels a lot like a desktop e-mail application: there's a preview pane, and messages can be dragged-and-dropped between folders. Right-clicking the mouse does mail-specific things instead of performing browser actions. There's no longer any concept of paging through your in-box. You can see all of your messages, no matter how many there are, in one big, scrolling list.
Besides e-mail, Yahoo Mail offers users built in instant messaging, weather reports, and an RSS reader that users can parse through as they would their e-mail.
Winner: Yahoo Mail (Mail.Yahoo.com)