Not yet mentioned:
Tuffmail
Rock solid! After a few years of no development Tuffmail is back in the hands of the original owners. SquirrelMail and Roundcube front-end. Most comprehensive admin console I've seen.
Rollernet
Comparable with Tuffmail. SquirrelMail and Roundcube front-end. Rollernet has a more technical approach and self-service angle than most other providers.
Pobox
My main account. Part of the FastMail family. Founded as a forwarding service. Uses FastMail's front-end. The best in spam reporting and spam filtering.
EuMX
Steady going, but outdated. However I do miss the OpenWebMail interface. Many webmail interfaces to choose from. Very responsive support.
Slashmail
Does it still exist? Yes it does. Roundcube interface. Not much in the news.
Soverin
Testing Soverin lately. A mail provider from my own country. Focused on privacy. Bits of Freedom, a leading digital rights organization in the Netherlands is using Soverin as their mail provider. Roundcube (modified) and Rainloop (simple and fast, like it) interfaces. Enthusiastic and knowledgeable support team, as far as I have experienced.