Jen Simmons is on a mission to get a new theme into Drupal 7 within the next 12 days called Bartik. Drupal 7 core co-maintainer Angie Byron said in the issue queue that "the deadline for new core themes is May 17, 2010 to allow for a few days to squash any additional bugs before the beta."
In this interview, Simmons talks about the evolution of Bartik and how she'd love to get some help in the Bartik issue queue. There's also a demo site that highlights the different features of the theme. If you'd like to see a new theme in Drupal 7, then be sure to jump in and get involved.