I use Hushmail as a separate account for sensitive data like bank/credit card statements, etc. I actually used a free account for a long while before upgrading so I could use IMAP access, as the web interface is useable, but not great. Though they do have an option to forward a stub email to let you know you have new mail, so that at least allowed me to notice if I had mail and check it. I'm not sure it's particularly more flexible, though-- at least, I find it more rigid and difficult to deal with compared to gmail, actually, if you're using the web interface.

(Personally, I'm playing around with Fastmail, which may be a decent switch from gmail for all my regular mail for me-- seems a bit more flexible in terms of filtering and search with Sieve, while offering additional services like file hosting. And it's pretty cheap, as well, which is nice.)