Picasa from Google is one cool piece of software to view and manage photos with ease. Till now, it was available for Windows based computer - Picasa for Mac is now out with beta tag. Being an initial release number of features are missing including: webcam capture, geotagging, online print ordering and export to HTML.
Also, the Photo Viewer software that accompanies Picasa 3 on Windows is not included on the Mac. Expect to see these features in future releases. Download Picasa for Mac (requires an Intel-based Mac and Mac OS X 10.4+). Here is video explaining it all: