When raising money for a startup, the most difficult question to answer is "What's your company worth?" I've seen complicated spreadsheets, anecdotal evidence and the most popular - the egos and hubris of the founders. But valuing a company is much like selling a house, the answer is simple, your company is worth whatever someone is willing to pay for it at the time.
Not very helpful.
However if we think about real estate, there is a better way to get at the answer. When you sell your house, the first thing you do is see how much houses are selling in your neighborhood. In fact whenever you finance a house you get a report of comps (comparable) of houses which sold recently with corrections made based on a variety of factors.
You can do the same thing for your company. The trick is finding valuations on companies like yours.
A few weeks ago a VC friend of mine directed me to a site which does just that. Venture Returns is a web site devoted to figuring out valuations. Not only do this have some nifty tools to help you do this, they also have a very nice listing of companies in every catagory. If you're still stuck, you can request comps in a very specific market and within a short period of time, they will give you a list. Highly recommended.