Google has introduced half a dozen new official Chrome themes, but you won't find them if you click the get themes link on your Personal Stuff menu. No, like the scores of user-created themes out there these new themes from Google have been dropped into the Extensions Gallery.
I'm sure the plan is to list everything in the Gallery at some point (possibly once it's re-branded as the Web Store?), but it really shouldn't be hard to give themes their own section on the existing Gallery. Or, you know, post them on the page Chrome takes you to when you click get themes.
The new themes are called Modern, Adaptive, Vibrant, Inventive, Fresh, and Orkut_Hudson. They're artist-created, and generally not for those of you who like Chrome's interface to be as unobtrusive as possible -- some are downright loud.
Beauty is in the eye of the beholder of course -- tell us what you think of the new themes in the comments.