Many versions of collet racks have been done, thought I'd show one I recently made for my 5C collets.
It's just a piece of 2 x 2 x 1/8 aluminum angle that I drilled 18 holes into. The aluminum is nice looking, light weight and easy to work with. Many ways to do the holes but the quickest and fastest was just a step drill. I made the holes 1-1/4 inches in diameter (for 5C's) and put a nice bevel on each.
I initially made this to mount to a wall or back of a door but when it was done, I noticed it fit inside my tool drawer perfectly so I mounted it to the backside of the drawer front.
Guess I'll have to do one for my R-8's and MT3's now!