I've immediately jumped on the new 6.5 release of the Netbeans IDE when it was released with much fanfare about its PHP support. Netbeans is a free to use IDE sponsored by Sun. I've used it years ago to edit XML documents, but did not look back on it ever since. Now it does indeed have nice PHP syntax highlighting, context sensitive code suggestions and debugger support as you'd expect from a PHP IDE. It does not look great on a Macintosh and it has some little annoyances which might not help you to use it, it is getting to be a nice tool for PHP developers.
Many of us are however not "PHP developers" or at least code mainly against frameworks, so support for our favorite frameworks in an IDE is even more compelling. Help in quickly starting development of Drupal modules and themes in an IDE could be very helpful for example.
Here comes Sujit Nair from Sun, who recently (last days of October and December 2008 respectively) published two plugins for Netbeans. The first provides a wizard for creating Drupal modules quickly, while the second helps starting out a Drupal theme fast. These plugins are still at their early stages, they do not allow you for example to pick base .tpl.php files to copy to your generated theme to start to work with, but I bet if these are picked up, the wizards will become more intelligent.
All-in-all I think Netbeans shapes up to be a compelling offering for Drupal developers, especially considering its price (free). I did switch back to Komodo, in part because Netbeans cannot soft-wrap lines for display and editing and the developers consider this a complex issue to solve, so we might not see it fixed soon. I strongly suggest however that you take Netbeans for a test-drive, especially if you currently only use a text editor to write code.