I also use numismedia and find those prices to be fairly close to accurate as well as the website having a good user interface.
On numismedia, any modern coin in circulated condition that they assign a value beyond FV is not really accurate. I'm referring to the G-F range...I know some XFs and AUs will carry a slight premium. Also at the other end of the scale...where some of those values come from are anyone's guess. They also don't list values for some coins in the highest certified grade.