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.
Encrypted, paranoid friendly email service. 3mb free, 75MiB accounts from $25/year. Not particularly cheap and very Web 1.0.
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.
Lists webmail providers including a list comparing features such as own domain, imap, pop3, etc. Makes a useful list when looking for an outsourced mail provider.
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. :)
BlueTie are a business email hosting company. Prices start from $5/month/user including 10Gb of space, virus, spam, calendar, etc.
Runbox is a mail hosting service, from $50/year, sub accounts at $20/year, extra domains $5/year.
Mail hosting company based in the UK. Accounts start from £12/year for a 1Gb IMAP / POP3 / SMTP box.
FuseMail is a hosted mail service which includes webmail, IMAP, POP3, calendar functions, shared files, groupware, and more. All for $2/month/mailbox. Great.
Google Apps is the hosted mail / docs / etc product from Google. It comes in Free or Premier ($50/year/user).
Zoho is an online office suite, similar to Google Apps. It includes a hosted mail product.
Zimbra is an open source email / collaboration software. They offer a hosted service starting from $400/year for 15 pro mailboxes.
Interesting web hosting company. VPS based hosting from $10/month including a dedicated IP and mailserver with webmail (squirrelmail / OpenWebMail).