Currently living with my bf and he makes about 2x as much as me...but that's a slightly different situation. However, I insisted that we split rent, groceries, gas, car insurance (since we share use of his car), and joint household purchases evenly (like, 50-50). People have pride. Also I'm trying to keep his standard of living even with mine.
Personally, I would share things like Netflix, Hulu, Amazon video, etc for free, but mostly because whichever of those I had, I would probably choose to have independently of my roommate's choice, and at that point it's no skin off my back if they use it...and it gives you karma points.
If for some reason you didn't want to split everything 50-50, one fair approach I have seen is to split rent weighted by bedroom area. Obviously this only makes sense if there's a reasonable discrepancy. The house I rented in for 4 years had a tiny bedroom, and while we had 3 people, the rents came out 200-300-300. After I moved into the larger room and we decided not to get a third roommate, we just did 400-400 because they were close enough (Yes, my rent was 200/mo for 2 years, it was awesome! but eventually the space got pretty tight when my bf visited). I could also see a similar approach being used for another valuable room commodity: bigger closet, window, bathroom, better view, whatever. Not saying you *need* to pay more, but if the income disparity makes you uncomfortable, this is a not-unfair way to justify unequal rent-sharing.