I wanted to make a rectangular box that locks well and is stackable - this is the result. The print-in-place sliders have a nice click when unlocking (due to some print-in-place springy thing), then the lid can be taken off. The sliders themselves have a bit of grip on your finger to pull the lid up, but optionally there's a fold-up grip ring, which also might be handy for pulling a box out when there are a couple of them side by side.

Since the lid prints upside-up you can easily add text to it. These boxes have a small rim on the outside, so they are stackable.

The print-in-place grip ring has some small built-in mini supports which need to be broken by flipping it up the first time.

I uploaded a couple of sizes (values are inside dimensions), but if you need a different size and lock configuration, ask in the comments and there's a good chance I'll upload it.

Printing: 

0.2mm layer height, 0.4mm nozzle, no supports.
I sometimes used a fuzzy skin (outside only) modifier block on the body part. 
If you want different colors for body and lid or if you want colored text without a filament changer, split the model into parts and delete the one that you don't want to print in the current color, print, undo delete or reload, then delete the other part(s) and print with a different color.