Mark referred saying that a valuation is determined by the demand for that particular service or good. You can certainly start by using a worksheet, like the one provided by Kauffman here (Valuation Worksheet and Fundability and Valuation of Startups: An Angel's Perspective) but you should not forget that its the market that will set your price. If your startup shows predictable revenue, you're in a great position to set a valuation based on that.

Tom quoted for us from his experience that these valuation worksheets are a nice way of trying to put a value to the various elements of a start-up but unfortunately the scoring in each section will generally come down to a split between data and the investors' gut.

Scorecard-Valutaion-Methodolgy was used before. It has a decent split of the different components of a start-up and how they should be valued, but again, this is just a guiding rule that puts a little perspective on things!