I'd go with NoSQL (any of them, overview of all of them?) or AWS/cloud stuff, because I'm already familiar with Linux administration and RoR. In the enterprise

I'd go with NoSQL (any of them, overview of all of them?) or AWS/cloud stuff, because I'm already familiar with Linux administration and RoR. In the enterprise you don't get to work with that sort of technology, so that's where I'd spend my time.