you can put any songs on, not limited by genre or anything, not even limited by what you think the other person will like. just make a good mix that has good flow. trying to find songs the other person has never heard will be very difficult, so screw it.
Firedwarf, if you think you can do the mix over the next five weeks or so, then that would be cool. otherwise you might want to hold off joining this trade just so the person who gets listed below you doesn't feel fleeced. (even when we had a deadline last time, some people [ahem chromelife] nevertheless trickled theirs in months later, so i'm wary about having NO deadline or a very long one).