As much as I love using Gmail, the Greasemonkey script-based Better Gmail plug-in made my favorite e-mail client, well, better. Integration with Google Reader, colored labels, built-in TinyURLing, and other features really made Gmail that much more useful. Since Google's recreated and upgraded most of Gmail's back-end, those scripts and most other Gmail plug-ins have broken.
To confuse matters, Google is slow in rolling out the new features, so not everybody is using the new interface. If you do have the new Gmail, you can access the old interface Better Gmail 2 v0.1 recreates some of the features in its predecessor, and promises to eventually feature most if not all of the old expanded functionality. For now, though, it's slim pickings.
So far, Better Gmail 2 has been able to recreate about half a dozen features from the old version. There's the forced https connection, useful for us paranoids but probably ineffective against the combined might of the U.S. government and AT&T. There's a forced mailto, as well, so that all mailtos in other HTML pages open up a blank e-mail window in Gmail. The Inbox Count First feature shows the unread message count from the in-box in the Gmail tab title, which is great for keeping track of incoming mail if you have a bunch of tabs open and can't view the entire page at once.
Other features include support for keyboard shortcut macros to expand the set that Gmail comes with, a place to set your domain for Google Apps, message details that appear only for the most recent message in a conversation, and attachment icons that replace the boring paperclip with the more useful program appropriate icon, so that a ZIP attachment will show a ZIP icon in the e-mail list.
Better Gmail 2 is off to a good start, but unless you're looking for one of the specific features that it provides, it's probably better to hold off downloading it until a more muscular version gets released.