Ryan Singer shared an overview of the design workflow at 37signals (makers of basecamp and highrise – totally awesome apps) at the Future of Web Apps conference.
The 37signals design process starts off by sketching out the model of the web app, then working out what user interface screens (defined by function) are required. Design is first worked out on paper, then BEFORE going to Photoshop, Ryan mocks something up in HTML/CSS so that the programmer can start building with the core elements. Then he takes a screenshot of his rendered HTML/CSS and adds this to Photoshop to build out the design. It’s an interesting twist on the usual Sketch > Photoshop > Code workflow that works with the simplicity of the 37signals interface.
Ryan Singer at Future of Web Apps, London 2010 from Ryan Singer on Vimeo.


