I have a project named Qusion that you can install as a rails plugin. Takes care of setting up EventMachine correctly for Passenger, Mongrel, Thin and others.
You might also like Warren by brightbox. It has some other whiz-bang features, but doesn't set up EventMachine on Passenger or Mongrel for you.
Workling also seems to be popular (you can use it with qusion if you like):
Assuming you weren't being sarcastic.... ;)
Dan DeLeo