I have chosen Fastmail. Cheap, works really well (but I am a new customer so more time needs to pass), you can register I think 100 custom domains on 1 account,

I have chosen Fastmail. Cheap, works really well (but I am a new customer so more time needs to pass), you can register I think 100 custom domains on 1 account, aliases, catch all addresses, etc.. They host caldav and carddav stuff too. Their webui is really fast, much faster than gmail, and IMAP works great. AND they can import your gmail account. They imported mine in a few hours, 4.5gb of mails.