Google Apps Mail
I've been using a web-based email program called Open WebMail for the past 7 or 8 years (from back when it used to be called NeoMail). But my spam flagging attempts have become increasingly less effective, and Open WebMail isn't AJAXy (which makes it slower to use), and Google Mail is pretty fantastic.

So I signed kingant.net up for a Google Apps account. I'm pretty happy with it. I imported all my mail from the past 8 or so years. It takes up 995MB (14%) of the max of 7035MB.

So far it's been reasonably reliable. There was maybe an 18 hour period around August 8th where it was down and I couldn't log in at all. But I'm hoping that was a freak occurrence.

And the spam filtering is pretty good. I still get 1 or 2 spam emails a day that aren't flagged, but that's better than the 10 or 20 I was getting before. I get about 11,000 spam emails per month. That's about one every four minutes.