+1 for Tuffmail. Also a long time customer. My favorite feature is the admin interface that lets you manage an unlimited number of aliases and route them to specific folders, e.g., foo@domain1.com => INBOX/foo/, bar@domain2.com => INBOX/bar/. Compare this to Google Apps and Fastmail, which both seem to limit the number of aliases you can create.
http://www.tuffmail.com/
Edit: It's not free. It costs like 2 dollars a month for the smallest account.