The site has large beautiful pictures of every US and UK classic stamp along with tutorials, a number of which I developed, to distinguish the many varieties of US classics as well as a wealth of other information about each stamp. For a more accurate assessment of current value based on the total range of grades, see the PSE (Professional Stamp Experts) pricing guide, which is updated quarterly. Their cert grading also considers other factors than just centering, such as shade, impression, eye appeal, the back, perfs, faults, etc. But it will give you a better idea of the range of retail values in the US Classics arena.
Google "SCADS" to go there. This item is in the category "Stamps\United States\19th Century: Used". The seller is "geokster" and is located in this country: US. This item can be shipped worldwide.