I was looking for this information when I was purchasing a house. I knew what my score was, and I knew what the "prime" interest rate was. What I didn't know was the average rate I should expect to get based on what my score was.
Here it is! A chart from bankrate showing just that.
if score was high**
I did shop around and went with the bank offering the lowest rate. That should have protected me against getting a poor rate, but it really didn't. When every lender gives you a high rate and one gives you a lower one, you tend to believe that the score you have matches the rate you are getting. It really didn't, and I am paying a higher rate than I believe I deserve. It may be time to start shopping around for a refinance, though I hate to go through the process again, and I'd hate to pay closing fees. Still, over the long term of the mortgage (I am assuming at worst case that I will not be able to pay it off as early as I would prefer) it will save me significantly over the long run.