I used Gmail for quite awhile, then started looking for alternatives. Inbox.com is decent, but has no IMAP, which made it worthless for me. GMX Mail also looks like it could be good; seems very similar to Gmail. I hear very good things about Fastmail, but usually from paid users; if you're using a free account, they only give you 10mb for storage.
I eventually settled on paying ~$20 a year to Tuffmail. The features (Bayes classifier, sieve filtering, company who actually cares about my mail, etc.) made the marginal price worthwhile for me. If I were to go back to a free account, it'd probably be Gmail; I haven't seen anything better than it yet.