RoundCube Webmail
Even though RoundCube is officially still in alpha phase it is a very usable webmail-client; replacing my previous SquirrelMail client, which is everything RoundCube is not. RoundCube uses AJAX combined with the Ilohamail IMAP classes, while Squirrelmail uses it’s own backend (which is faster) combined with a frontend based purely on HTML tables. Although Roundcube suffers some performance issues, it’s clean PHP code and templating system make this a very nice webmailclient with lots of potential.