Whoa - let's hold on here just a second - and take Mark's words to heart - you can really get burned here if you aren't careful.
I have State Farm insurance on my house, my car, my wife's car and my two daughters' cars. I have my '69 RS and my '66 Chevellle insured through a firm that deals with nothing but classic cars - and for a very good reason.
Yes, State Farm will issue insurance on a classic vehicle per an "agreed to value". They even have run ads in Hemmings and other places touting their coverage.
The "gotcha" is that unlike my current coverage, which will pay the "agreed to value", in all cases, for either of my cars if they were in an accident, were totaled, and deemed not repairable, is that if you have a claim with State Farm, they may not necessarily pay the "agreed to value". What they will pay is the "actual cash value" or ACV of the car at the time of the claim. This is a subjective determination made by the State Farm adjuster. If in his/her opinion the ACV is less than the agreed to value, you will get less than what you were expecting. Point to remember is that, in all cases, from State Farm you will get ACV at the time of claim. Whether or not that will actally be what the previously agreed to value is will depend on the State Farm agent and adjuster involved. It is for this very reason that I have my '66 and '69 insured elsewhere.
In general, the folks that deal specifically and only with collector cars make it pretty easy. Most of those policies are set up where the agreed to value is what you get if the car is totaled and not repairable. In any event, make sure that you understand the fine print.