Check the privacy policy of any provider BEFORE you sign up. I get nothing but junk mail from Yahoo and hotmail. But the 6mb mailbox at Yahoo and it's integration with it's IM client make it attractive.
I use zfee.com .They offer a proxy server as well. They respect your privacy & won't reveal anything without a court order. They may or may not suit your purposes, but the real reason I use them is the full-screen reading window for e-mails. No ad frames & no in-box rosters cramping my space. It's nice for looking at pictures, you don't have to go scroll crazy.
I use Onebox for most of my e-mail. It's even supplanted my regular e-mail service. There's a good bit of space free, and they offer a few other perks, like a handy phone message service, too. The server's fast and I don't get spammed.
For those communications you want to keep secret, you can try ZipLip . It's a very handy encrypted e-mail system (though you can also send regular e-mail too), that allows you to send someone an encrypted e-mail and have them input a password on their end to read it. There's a couple different ways you can do it, and it's kind of handy. The regular mail features are pretty good, and I've never had spam there either, though it's been a *long* time since I've used it.