While perousing the isles of OSUsed (the campus surplus store here at Oregon State University) A friend of mine found these great little bottles, from the chemistry department, appearing to be made of pyrex.
They have threads on the neck, but no cap, and seeing as I have a MakerBot, I figured it'd be a good idea to make one!
A bit of quick design (and a couple failed attempts) later, I had a cap!
The cap works great, not waterproof yet, but a quick dip in acetone would fix that... For me they'e mainly decorative, but I could see them being quite usefull!
Designs are Here!