At the startup where I work, we use Amazon. Start with a small or micro instance and put Cloudfront in front of it. As you grow, add more instances behind a l

At the startup where I work, we use Amazon. Start with a small or micro instance and put Cloudfront in front of it. As you grow, add more instances behind a load balancer and switch your databse to a master/slave setup. Add memcache to cache queries, and use Varnish as a caching proxy. That's how we started, and after a year we hit 200+ instances and growing (you'll have to request an increase from the 20 instance cap, or split them across accounts). EDIT: we are working on a big data app, so most of the horsepower is for crawling and number crunching. 10 instances are client facing