epitome

http://www.google.com/apps/intl/en/business/index.html

I got in for free in the beginning when anybody could. I get up to 50 accounts with 8 GB of storage for free, as well as everything else. I think they're charging $50/yr. per account now (you get more storage with that) but it's still very well worth it. All you need is one and then you can have up to 5 aliases where it will combine all domains in your inbox and your outgoing email can be setup to match whichever domain you want.