I picked up another nice specimen recently, a Hartford (CT) High School bond. The vignettes on this one are quite attractive, considering it was a mundane municipal bond.
The other two are not specimens, per se, but I thought it would be useful to illustrate different types of certificates. This one from the Mutual Banking Co. of Richmond is a printer's proof. These were typically printed on card stock and punch cancelled at the bottom. They were generally used just for in-house review by the banknote company.
Lastly, here is what's known as a blank. These were printed by a large banknote firm (American Bank Note, in this case) in advance with partial or no text, then either sold to a local printer or used for small jobs. I've seen a completed blank similar to this for the Delaware Railroad.