Some pre-pro collectors restrict their acquisitions to glass shots but if you want to add a little diversity to a collection, other type of shot 'glass' are available.  Most common are the metal shots, which come in three basic forms - Thimbles, Aluminum cups, and Telescoping Cups.

Thimbles:  I really have to wonder if anyone was actually amused by the tippler who insisted that he was "only drinking a thimble-full" and then pulled out an oversized,  two-ounce thimble, but apparently someone thought that they were cute.  Unbranded thimbles in aluminum and sterling silver are easy to find.  Occasionally, a branded thimble comes up for sale with the message being embossed in the base and/or inscribed around the mouth.  Some examples are shown below.