Boy I'm tired of mixing by hand. I could do the drill trick that CLC mentions but i'd love to find an automated mixer. There are several I've seen on Amazon and such but they are in the 50-100 ml range, looks like for arts and crafts stuff. I have also seen a few for larger volume ones (up to 1000ml and more)  but they are pricier. 

Before I haul off and buy one, I figured I'd ask if anyone else has had any success with these contraptions. 

If you have a good rec, i'd love to hear it.