[AngryParsley]

EC2 is the only provider where you can make API calls to launch 50 servers, have them all booted in a few minutes, then shut them down an hour later. Slicehost's management console will barely load if you have 100 instances, and your servers are all in a single data center. Ditto for Rackspace Cloud. (Both have multiple data centers, but each account is bound to one DC.) I haven't tested Linode beyond booting a single instance on it, but since they bill by the month I assume they're another cloud-ish VPS provider.

Of course, most individuals and small companies would do best to pick a cloud-ish VPS provider. They have much better support than EC2 and small companies usually don't need hundreds of servers.

[commx]

While Linode's billing is monthly by default, it's also prorated. This means that when you remove a Linode from your account, the account is issued a prorated service credit for the unused time in the billing period. Service credit is always used for further services before charging the card on file.

In other words, you can spin up multiple Linodes, remove them the next day, and all you're really paying for is the day you had them deployed. There's a document on Linode billing located here: http://library.linode.com/linode-platform/billing/

[byoung2]

EC2 is the only provider where you can make API calls to launch 50 servers, have them all booted in a few minutes, then shut them down an hour later

GoGrid (http://www.gogrid.com) also has this ability (they also have cloud-based F5 load balancing and mountable block-level storage). They have datacenters on the West and East coasts, and you can pick one when starting an instance.

[commx]

I should have also mentioned that the Linode API supports what you're describing: http://www.linode.com/api/