I\'ve used straight Mongrel, I\'ve used Mongrel clusters behind Apache, I\'ve looked at Thin, and I\'m becoming very intrigued by Passenger. I\'ve looked at Nginx, too. I\'ve lo
I'm hosting my new apps with Apache2 and Passenger on Ubuntu Hardy. Seems like the easiest and best option for most scenarios. I have just joined Slicehost.com for that purpose. They seem to get good reviews and have the most competitive prices of first class hosts.
I can't really endorse them yet because I'm a new client but the set of guides and range of support options is impressive.
What you are not mentioning is how large and popular your app is/will be. This criteria could affect the decision process.