Email solutions... what's out there for IMAP and (preferably) free?

[exi]

Title says it all, really.

I'm currently on Gmail; I was there before they rolled out IMAP support, and I was pretty happy about it when that came out, too. Given that I'm using a Diamond but also defer to webmail and/or a client of the week (Outlook 2007 / Thunderbird 2), IMAP is the logical way to handle things. I'm too anal to have to mark the same message as read twice, etc.

I have three Gmail accounts that forward to one of the three, along with a university email account (currently forwarding to that one Gmail address).

I'm big on folders, but that's just not an option with Gmail outside of a client (yeah, labels are there, I know). But anyway, what other free IMAP services are available?