OpenSCAD file for making round trays. I created this to make small trays for screws and other small parts, but the parameters can be changed to make other similar objects (bowl, cups, etc). A few example stl files are included.
For square trays, see http://www.thingiverse.com/thing:43406
For round trays with lids, see http://www.thingiverse.com/thing:44535
The lids are compatible with these trays as long as the sidewall and diameter match.
Use the "Open in Customizer" button to make your own version. The changes will propagate faster at low resolution, but the resolution can be increased for final output.