Just downloaded the latest beta (3) of the Google Toolbar, and I have to say I'm pretty impressed.
The coolest of the three new features is the Gmail style form spell-checker. It's a great leap forward for web-app developers, who will no longer have to provide their own spell-checkers independently (Yes, Firefox has a spell-check plugin as well, but it's of poor quality, like Blogger's). So, seeing as I was just recently ranting about Blogger's horrible spell-checker, I'm happy to see Google take this out of the web-app and put it into userland (also lets you keep a single dictionary across multiple sites).
The AutoLink feature, which finds text addresses and turns them into clickable links to Google Maps, seems to be pretty useful as well. I heard about a browser plugin that does something similar for phone numbers and Skype, and I'm sure we'll be seeing lots more of this type of thing quite soon.
Then, of course, there's the word translator. It's pretty neat, but seems to be limited to only a few languages, and is probably more useful at this point to those who aren't fluent in English.
Go Google! Keep on innovating!
This post spell-checked by Google Toolbar beta 3