What two currencies [other than the US dollar] trade in close lockstep with one another, but not in lockstep with the dollar? What would be best for my purpose would be one currency that is actually pegged to another.
Estonian kroon is pegged to the Euro. Very stable since it was introduced in the 1990s. (Not to mention a lovely little country...)
The HKD is currently trading outside of it's peg range. I used to trade it but right now it scares me to death that it could be revalued.
Oanda has EUR/DKK, currently quoted at 7.4624 / 27. Use their demo platform (FXGame). Edit: here's a daily chart YTD. Don't know what happened on May 16th...