Lots of people have suggested 3D printing propellers, but Landru is the first I've seen to do it. Looks pretty good! (I'm not sure I'd trust my old Makerbot with this--he's got a better printer.) He writes:
This is a redesign for an 8040 printable propeller with a 5.5mm (13/64") bore.
This prop was designed to keep the minimum cross section above .8mm allowing it to be more easily printed, though at a small efficiency loss.
The propeller will require support on one edge, which makes it very easy to remove.
I can redesign this for some different center hole diameters if requested, just give me some time as I am pretty busy.
Here is a short video with the prop on a motor:youtube.com/watch?v=v6yClT12Ges&feature=plcp
I will also be uploading a 5030 prop once it is flight tested.
I printed mine on a Fablicator using Kisslicer.