The latest version is U.S. $199.00, and upgrades are available for any existing Aperture users for $99.00.
Apple says Aperture 3 has "more than 200 new features", including Faces and Places, brought over from iPhoto '09. There is an enhanced tool called Brushes, which allows photographers to paint adjustments and filters directly onto their images using new enhanced edge detection.
This latest version of Aperture runs in 64 bit on Snow Leopard and 64 bit processors.
Aperture has been in a long features war with Adobe Lightroom, a similar and very popular application. Aperture was last updated in February, 2008.
We'll have a close look at Aperture 3 when we get our hands on it. Apple has a free 30 day download for people who want an advance look, but as of this writing download links haven't yet been provided. Aperture 3 needs an intel-based Mac, so older machines like the G5 are out of luck.