Via LiveJournal found some fantastic looking web mail systems. Unfortunately out of three – one looks too much like default NeoMail skin, one needs its own web server and another one is still in early alpha (as it looks from Bugs page on SourceForge).
But look at the screenshots!
Zimbra: http://www.zimbra.com/products/screenshots.html
IlohaMail: http://ilohamail.org/main.php?page=ScreenShots
and my favorite – RoundCube: http://www.roundcube.net/?p=screens