I've been really looking for good alternatives to Google Apps recently - ideally, self-hosted with backup (highly encrypted) to S3 or such.
I'd use my server for this, but I've yet to find an email interface which even approaches Hotmail, let alone Gmail. I've been considering doing a clone of part of the gmail interface, but need time to read up on making sure email is less likely to go to spam.
Since I've moved my email to my mobile device, I've switched back to using regular IMAP on my computers.
Google refuses to release optimized versions of Talk or Gmail for iOS, I suppose so Android can have exclusivity, but it seems like an insane strategy. The Google app for iOS is Webkit garbage.
Now I use Lavabit for email. Their web interface is garbage but their security and support are top notch, and they will host mail for third party domains if you ask them to.
If you want to do e-mail syncing on most mobile devices, NuevaSync[1] provides an ActiveSync interface for any IMAP-capable e-mail account. I'm using them to do calendar sync to a device that doesn't do iCal and the service has performed quite well. Nueva even offers device wipe as an included feature.
1 - http://nuevasync.com/ .. I have no affiliation other than being a customer at $15/year.