I use .Mac. Have been since it was iTools. Paid my $50 discounted initial fee, then paid $100 a year later. Indispensable for having an access-anywhere storage, even if it is only 100MB (I use it to test web pages and transfer small files). My mac.com email address is my pride and joy, and am happy to say that I've kept it spam-free for years now by being careful whom I give it to. The free stuff is cool as well -- got a cool marble game, over 500MB of free sound loops, and free Virus protection (which I don't use, unfortunately).
Other places offer much cheaper stuff, but not with the tight Macintosh-integration that .mac uses. I don't mind the fee, and despite news sites reporting outages constantly, I've never experienced one. My iDisk always works, my email always works, and I think I'll be renewing once again in September.