The Summer '09 release of the Force.com IDE contains the following major new features:
Find all the details in the Force.com IDE for Summer '09 Release Notes.
Ready to upgrade? Just open the Force.com Start Page (Help > Show Force.com Start Page) and click Check for Updates. Detailed instructions.
First time user? Follow these instructions to get coding with the Force.com IDE for Summer '09.
Want to learn more? Read An Introduction to the Force.com IDE or visit the Force.com IDE home page.