Give them to your wife for her legs and such? Melt it down and make a shiv? Use it to shave around animal's wounds?
We have a thread laying about here somewhere in which one of the guys tells how to get more mileage out of your razor and keeps it from getting dull so quickly. I don't know if I'd ever heard of or even contemplated repurposing a used razor but I'm sure it's being done by someone out there.
Two threads with lots of info on them. I've been using the same mach3 razor on my legs and such for ohhh... a month or two now (probably about the same time I started that other thread! ) And I don't think I've noticed a difference.
We also ordered blades from the dollar shave club that was recommended in one of those threads. Not terrible, but not great, either. I've gotten 2 shaves of my legs out of one blade, and I think its still doing ok. I rub it against the blade up my arm when I am finished after making sure its good and clean in hot water. Dunno if that helps or not, but *shrugs* takes no more or less time! The blades certainly are a good price, even if the quality isn't super good.
This isn't really an answer of what you can use them for after but:
the Recycline company in MA takes #5 plastic (mostly Stonyfield Farms yogurt cups) and makes their products with it. They started with razors and toothbrushes, now they have kitchenware too. When you are done with the razor or tooth brush you can send it back to them, they are then moved on to a company that makes recycled plastic wood for picnic benches and such. It is a nice circle that I wish more companies would invest in...partnerships with other companies to make less hit our landfills.