I'm working on the executive summary for my website idea and need to figure out the total market capitalization for the this industry.
For example, if all the yearly advertising (and other) revenue of Yelp, UrbanSpoon, OpenTable, Zagat, etc. were all combined, that would total out to the total available market for the online restaurant review industry.
Any specific websites, key words to look for, firms that provide this research, or any other specific/concrete tips that would help me get the answer to this?
Keep in mind that I am NOT asking how to valuate or determine the market valuation for a specific business or company, but rather what the entire industry is "worth" in terms of total number of users X the average revenue per user (ARPU).
IF the goal is to attract the potential partners, TAM and SAM are not as important as customer validation.
A market may be addressable, but that doesn't necessarily mean that the constituent parts are willing to pay for something that will support business operations.
What you need is interaction with the particular customers within your SAM and validate that what you intend to offer is something that is of value to them - and what they are willing to pay for such a product.
Such research can be done without the product being built - but like Joel mentioned, it is a good idea to at least have some sort of online presense i.e. launchrock.
Once you validate customer desire + willingness to pay, then you have a defensible SAM. Once launched, you then tweak reality against research, and then have customer traction against your SAM - and a stronger position to present to VC types.
In short: Markets don't pay - customers pay. Find & follow the money.