EC2 plug-in seems to have regions hard coded. As more regions are added, these will have to be added to the list. Instead, it should retrieve all available regions through one API call, that way there would be no list to maintain.

The problem code can be seen here:

https://github.com/jenkinsci/ec2-plugin/blob/master/src/main/java/hudson/plugins/ec2/AwsRegion.java (lines 19-23). It should get all that info with the API calls, not through hard-coded enum kind of thing.