http://www.01.com/
Email / Zimbra hosting from 01.com. Starts from about $50/mailbox/year. Optional "Legal Compliance" service that archives all incoming / outgoing mail permanently for $25/mailbox/year. Nice feature.
http://safe-mail.net/
Encrypted, paranoid friendly email service. 3mb free, 75MiB accounts from $25/year. Not particularly cheap and very Web 1.0.
http://www.tuffmail.com/
Tuffmail offer an exceptionally advanced mail hosting service. The feature list is very detailed and very technical. All accounts are monthly bandwidth limited (related to the disk limit). Starts from 1 account at $2.40/month.
http://www.mailcircuit.com/
MailCircuit hosting starts from $10/year/account (minimum of 5 accounts) plus $150 setup on your own domain. So $50/year plus $150. 10Gb mailbox, etc. They have a handy list of their competitors. :)
http://www.bluetie.com/
BlueTie are a business email hosting company. Prices start from $5/month/user including 10Gb of space, virus, spam, calendar, etc.
http://www.runbox.com/
Runbox is a mail hosting service, from $50/year, sub accounts at $20/year, extra domains $5/year.
http://www.simplymailsolutions.com/
Mail hosting company based in the UK. Accounts start from £12/year for a 1Gb IMAP / POP3 / SMTP box.
http://www.eapps.com/
Interesting web hosting company. VPS based hosting from $10/month including a dedicated IP and mailserver with webmail (squirrelmail / OpenWebMail).
