Web designers out there are probably going to find a service like this one appealing. Basically, what the aptly-named GetSignOff website does is to let you have a way of presenting website designs to interested parties while keeping track of the different steps of the process, culminating with the sign off of the design itself.
The way this solution is put into practice is actually described step by step on the site. All the necessary items are touched upon – you can create clients and assign projects to them, and upload designs along with explanations of your design's approach. It is even possible to add notes direct to the design itself. Then, using the featured integrated comment system, you can discuss the design with the client. A nice touch is that each comment is stored for future reference. Finally, you can use the provided feedback in order to revise the design and post a new version. Once the final design is agreed upon, the client can sign it off.
If this approach sounds interesting to you, it is possible to create a free account and get started very easily. Just point your browser to getsignoff.com and start designing.