We are looking at Zendesk. Heard good things about it and think it might just be the ticket. I have used the "Free" version, but the $19/month one agent might work for us instead. You get the flexibility of your own email address (your domain).
3 karma · joined August 4, 2008
http://www.zuora.com/products/z-billing-product.html
<disclaimer: I met the founder once, but have no affiliation with the company.>