Enable customers to manage server configurations using something like Chef or Puppet.

currently I only seem to be able to have one ssh key per user. I want more!

Enable resizing of a Server from one ServerType to another, rather than having to snapshot and create new server.

Enable API users to receive callbacks on the progress or result of certain API requests.

If you add/update your ssh key after an instance is created then the key is not added to the instances config area.

An AWS style cost calculator (http://calculator.s3.amazonaws.com/calc5.html) to be able to generate estimates.

Sample server setups would be a nice to have, but for me the ability to save estimates and link to them for clients would be super useful.

See

Callbacks could include HTTP ping to something or even an SMS (via AQL + pass the cost on to the client/user) .. should the number of responsive servers in a LB group drop below a given point etc.

Ideally would like a place to also store files, so an alternative to s3 would be nice.

http://incubator.apache.org/deltacloud/

It's restful and written in Ruby, should be a doddle to implement, tempted to try it myself.

Enable [temporary] disabling of API clients.

There should be a way of printing all of the server's public ip addresses whilst logged into that server.

The reason I use Brightbox and EY cloud are so I don't have to build a stack. It'd be the clincher for me as I would rather leave the building of a stack to those who do it best. An nginx version of the stack would be great too.