A very quick & dirty first attempt at a simple stand for a Pi 3B, in the style of the delightfully simple yet aesthetically pleasing Pi Zero stand from Adafruit;
I wasn't necessarily expecting this to balance first try, but it's actually fine - if anything the base is unnecessarily large. Mounts using 2mm standoffs. I haven't actually tried connecting HDMI yet, the bend to get the cable through the hole may be too tight. As I said, quick & dirty first attempt!
Filaprint Premium PLA
I printed without supports, with the front (the surface with the holes in) face down on the bed of the printer. The angle is 30 degrees so should print fine in PLA for most people without supports.