I forgot the name for collecting paper currency (numismatics?) Anyway, I am trying to collect the smallest denomination of paper currency from every country!
I've had a lot of help (here in Utah) strangely enough by just going downtown to the bank's foreign currency exchange and they just give me whatever they may happen to have in stock at the time there! It's kind of fun because I'll never know from week to week what countries show up.

I'm still a loooong way from having anything near every country (over 200 just in the United Nations I think) but still, it's kind of fun to collect. Yes, almost as much as casino chips! hehe