Cant go wrong with the afore mentioned Gmail using IMAP.
Clay
Not to get picky -- I generally like and use Google stuff to some extent, as does everyone -- but as nice as GMail is I *do* have a couple of issues with it.
1. The ads. I don't like ads in my outgoing mail, particularly ones I haven't approved.
2. The keyword scanning. Google scans your email, picks up on keywords, gears the ads towards them. And who knows what else.
So yeah, Google's great but there's a catch.
Having said that, at least they have the good sense to be IMAP, so if that would be useful to you, it's definitely a fine option. ABH (anything but hotmail).
I personally use MobileMe. I certainly wouldn't find it worth the money if I was JUST using it for email, but its definitely worth it to me for all that it does, from ad-free email to photo galleries to the iDisk to Find My iPhone (etc). If you're getting rid of your domain, you might consider MM. It's not free, but if you shop around *coughAMAZONcough* its pretty cheap.