When I have the locker do it, I have them use either one third beef tallow or one third pork. For burgers, I prefer the tallow. You can also just grind your venison and mix 50-50 with hamburger. If you use hamburger, don't get the high priced, lean kind. You need the higher fat stuff to help bind the low fat venison.
My son likes his venison with no binder, but he uses it as loose meat (tacos, spaghetti, maidrites, etc.) rather than patties.