It all depends on what you have, really.
Railcraft tanks are really iron-hungry, the Low pressure boilers also require quite a lot of it, steel for High pressure boilers also comes from Iron.
If you still have way too much, you can have fun with Modular Power Suit, as most modules cost a fair bit of it.
If your build style allows for it, you can use Iron blocks (and the micro blocks made from it).
As I said, I have no idea of what you have, or what "too much iron" refers to.
I personally never have enough of it, because I love Railcraft, making rails, tanks, Steve's carts carts...
If you are really way into endgame, you might want to use EE3 or Thaumcraft to get what you need that requires Iron as a base too.