As to the first cover posted (USPS Emblem - Scott #1396) this web site has a search function that identifies virtually all of the postmarks and their specific value, as some are worth more than others, although most have only nominal value. Unique to this issue was that every post office in the US cancelled these stamps on the first day of issue, so there are something upwards of 33,000 different postmarks available for this stamp:
http://www.remcatalog.com/Default.aspx