Countermail is good, but damn, they are fussy about PGP public keys. They have the worst system for exchanging keys with non-Countermail users I've ever seen. I actually groan in anxiety when I see an email from a Countermail client in my inbox, because it's going to be a chore to get their email to work with mine, every time.
secure-email.org is superb; I might move to them if anonymousspeech proves to be less secure than I'd hoped. They're in turkey, so unlikely to cooperate with USA, and they're highly encrypted and anonymous.