One of the major technology revolutions that's really been picking up steam lately is cloud computing: hosting on multiple virtual machines rather than fixed hardware.  Allowing dynamic scalability and on-demand performance, cloud computing has pushed the cost of start-ups dramatically down.
 
Google App engine is currently a free offering from Google (expected pricing has been announced).  Since launch, they've continuously released new features.  I've been particularly anxious about their release of PHP - the platform currently only supports python. 
 
Google App Engine Blog: Google App Engine Roadmap - Now Published