Google has some great apps for mac's and here are some of them. Google desktop I had on my pc and found it really useful and loved most of the widgets that were available now its also availabe for mac's.

Google Desktop For Mac

Find and launch applications and emails from your desktopAdd Google Gadgets to your Dashboard and iGoogle pageDevelop and share new Google Gadgets

Google Picassa For Mac

Manage your photos in one place, and find photos you forgot you had
Eliminate scratches & blemishes, fix red-eye, crop and more
Turn photos into movies, collages, slideshows and more

GMail Notifier for Mac The Google Notifier is an application that shows you alerts in your menu bar, so you can see when you have new Gmail messages or upcoming Google Calendar events without having to open a web browser.

Google SketchUp For Mac use Google SketchUp to create, modify and share 3D models.

Toolbar for Firefoxadd a search box to your browser and block pop-ups.