So there is this new tool coming out whenever called macaw. Quite a few people were raving about it on twitter and it is definitely something that I would like to try out once it's available. It looks pretty promising for putting together a mockup, not sure if I would use it for actual coding, but to me it seems a lot better than having to switch back and forth between the browser and Photoshop.
http://macaw.co/
http://macaw.co/