Mailplane brings Gmail (Google Mail) to your Mac desktop. 

 It combines great Gmail features like Google Search, conversations, spam protection, and the unique Gmail interface with the power of your Mac: send pictures from iPhoto; create attachment by "drag and drop"; use multiple accounts; get powerful new mail notifications; and much more.

For more information check the home page, How-to articles, FAQ, Support page, or watch the screencasts. 

Download Mailplane.

Try and test the latest preview build.