I enjoy collecting postal history and various uses of the 2nd Bureau series of stamps. Used blocks off of cover are fun to hunt for, and I am always looking to upgrade. It is easy to find used multiples of four our more of denominations from 1c to 15c; however, the 50c and dollar stamps are difficult (and expensive) to acquire.
1c Franklin (300)
2c Washington Flag (301)
2c Washington (319)
3c Jackson (302)
4c Grant (303)
5c Lincoln (304)
6c Garfield (305)
8c Martha Washington (306)
10c Webster (307)
13c Harrison (308)
15c Clay (309)
50c Jefferson (310)
$2 Madison (312)
1c Franklin Imperforate (314)