I love Twenty Ten. (Really, it's what I was thankful for this Thanksgiving). The theme's structure, typography and general functionality make my mouth water. It's more than "just another WordPress theme." The best part: It's so damn versatile. With just the addition of a file or two (a stylesheet and sometimes a loop-index.php), the theme can be transformed into a whole other animal. Here are some of the ways I've tweaked Twenty Ten for freelance projects and for friends/family to quickly make WordPress sites that are compatible with all of WordPress's awesome features.
*Note, this one took significantly more tweaking than just a css file and loop-index.php at the request of the client's specific needs. It's still a child theme, nontheless.
I want to see other uses of Twenty Ten. If you know of 'em, share your links in the comments. And if you aren't using the theme, try it. Child themes are fun and easy, and Twenty Ten has all the basic features you could possibly want for a simple blog. As shown in the examples above, you can even use it for more complex sites. It saves serious amounts of time and always looks slick, even if you don't make any modifications.