FastMail has been on a roll lately. In the past 12 months they've added CalDAV and a terrific web app for calendaring, CardDAV support of contact management and syncing, IMAP Notes support and now comes the long awaited IMAP email push.
Push email will happen automatically for existing users and if you already have iOS configured with FastMail IMAP, you'll just start benefiting from the change without doing anything extra.
This month marks the 2-year anniversary for FastMail and I. It's been my sole provider for personal email in that time. All of my other accounts route to FastMail and they handle all server-side mail rules, spam filtering and syncing to every device. Their web app is fantastic and their support has always been excellent for me.
If you want to check out FastMail and support this site at the same time, here's a referral link that costs you nothing.