Gmail.
I'm not sure how closely everyone else is following this, but I'm thrilled. The privacy concerns don't bother me -- you're foolish if you're keeping highly confidential information on a free public email system. The storage is nice, but I'll probably be a light user in the respect. The thing that clenches the deal for me is the cleanliness. The interface looks to be what I've wanted email to be for years. Conversations in context, easy labeling filtering, and of course google's amazingly quick search through my email thanks to there home-brew file system GFS.
Gmail Interface Related Links