It’s a GMail-specific mail client for OS X that captures the spirit of GMail pretty well, and keeps everything perfectly in sync. You can archive or delete messages, tag them, even manage multiple accounts from a Tweetie-style sidebar. (The application actually takes a lot of design cues from Tweetie/Twitter.)

It also works with Google Apps accounts, so you can use it for your domain email.

Sparrow is a very nice email client, and is available in the Mac App Store for a reasonable price. I’ve been using it out since the last week of the beta, and it has convinced me to stop using the GMail website for my day-to-day email reading in favor of Sparrow. It complements the iPhone email client nicely in my daily workflow.