We don't really designate much in our house as "just for boys" or "just for girls." Elena has just as many bats, balls and golf clubs as Sam (although hers are rarely touched and Sam would play ball for hours on end).
Sam plays dolls with Elena (although he usually gets quickly distracted with figuring out how the buckles work on the doll's carrier).
If Elena gets toe-nail polish and Sam wants some, I'll put it on him (Seth's not a huge fan of this, but he tolerates it :)
I've read books about trucks to Elena since she was little, but she rarely asks for them again, and I had never heard a real "truck sound" in our house until we had Sam (if I did, it came from Seth).
I recently bought a box of antique cowboys and Indians for the kids at a garage sale. The only reason I got it was because it included a horse and detachable rider that I knew Sam would love to play with (he loves horses). Anyway, they haven't played with them much - Sam will occasionally have the people on horses run around, but that's about it.
The other day, Elena pulled out the box and decided to play with them. And what does a little girl do with a set of cowboys and Indians?
Well...they do make a great rainbow.