Nondenominated postage

[cjsmith]

I don't mail physical letters very often. I don't buy stamps often, either, and I rarely know off the top of my head what the US postal rate is for a first-class letter. When the stamps themselves don't in any way indicate what they're worth, and I have an eclectic assortment probably dating back to the mid-eighties, that adds an extra dimension of fun.

This page is very useful.