Mac users using Gmail or Google Apps should take a look at the Sparrow mail app. It puts a Tweetie for Mac-like interface on top of Gmail, and is doing so with increasing effectiveness. The latest beta tightened up the design, improved performance, and added support for e-mail aliases on an account. It’s the first mail client I’ve used for consecutive days for several years. While I’m not sure it’s the best choice for people who need to manage a lot of e-mail (there are some issues with deleting and archiving many messages at once and no support for labels yet), it’s now good enough for my purposes and I’m looking forward to seeing it evolve further.