Is there a eco-friendly method to dispose of brake rotors and brake pads?

Put them in the recycle bin. The metal is as recyclable as any other thing, like aluminum or what have you. If you are worried about what's left of the friction material on the pads, just take it off and throw it away. The friction material wouldn't be recyclable, but the backing material would be. Rotors are just iron and can be recycled just as well.

Could take then to your local garage, they have to re-cycle their waste parts responsibly. I don't think my local dustmen would be too impressed by big vented discs in the bottom of my recycling!