Tank swap? What other tanks fit?

I'm interested in changing up the look of my bike. Something I would like to change the style of if the tank. Does anyone know what other tanks might fit, something off of a different bike? I was looking before at tanks for a Honda Varadero and was told that the Superhawk tank and the VFR tank was a straight swap. I was told that the VFR tank was a fairly popular mod on the Hawk since it's a higher capacity and they're a thirsty bike.
Does anyone know for sure?

Thanks.