I got an invite from Tom Morris a few days back for MailPlane (why do you need an invite to download a beta app? just because it IS an invite?) and I must say I like the tool a lot. MailPlane is basically an Application wrapper for GMail, enabling you to have a Mail like app that allows you to drag and drop attachments into a GMail email and much more. It is still in Beta and definitely not complete, but give it a try. I have 4 invites left, so drop me an email to have me send you one.