What don't you like about the full Outlook? Much as I dislike MS business practices I have to say the Outlook is pretty good.
Having said that, I'm happy with Thunderbird (the companion to Firefox) and even happier with Opera, which combines a browser and email client.
Opera is free, secure, very fast and properly W3C compliant - the email client is very configurable and robust. As I've said before, if I wasn't so hooked on my Firefox extensions I'd change over to Opera completely.
Oh, and Opera is fully cross-platform - looks and behaves the same way no matter which OS it's installed in - Windows, Mac, Kinux, FreeBSD, Solaris, OS2 or QNX.
See
http://www.opera.com/
