We keep teasing you with news about the as yet unreleased Mailplane, but this excellent dedicated Gmail client just keeps getting better. The latest update to 1.46 adds several very cool features, most importantly multiple account support. You can now use Mailplane to access different Gmail accounts, simply by double-clicking the account name in the drawer. This release also adds a menubar notifier, which very cleverly includes multiple accounts at the same time so you can check for new mail easily from either account. Finally, there's also a new text snippet feature that allows you to easily insert often typed text.
I've been using Mailplane for a few months and I must say that it is shaping up to be a stellar release. It's one that I'll spend my own hard-earned money on when it comes out. Unfortunately, Mailplane is still in closed beta, but you can apply to be a beta tester.