If you are looking for a paid service, I personally use Beckett organize tool, it is quite helpful for me to keep track my "assets". It is quite a pprice tag for a yearly membership, but you get a full online price guide; and if you divide it by 12, the monthly cost is less than an average Panini pack or two
For free service or app, I have no idea...if there is a good tool I might want to use it