The US is having a cent redesign next year and coming out with a new Native American $1 program. I know the cent is supposed to have 4 designs. I haven't heard much about the $1 program.
In the meantime, I know you like world notes. Have you gotten one of the new US colorized $5?

Personally I think Euros might also be fun to collect. I think I'll try to start getting some soon. Here's a link that's helpful if you're considering it:
http://www.eurocoins.co.uk/