Some of my minifigs (like Iron Man, and Bilbo Baggins, and Harry Potter) have two different faces to show different emotions (usually something happy and something unhappy or upset or angry). How long have they been doing that? What was the first minifig to have 2 different faces to choose from?
A quick search on Bricklink gives the following results:
Catalog: Parts: Minifig, Head: Search Results for dual sided
This search was caried out at http://www.bricklink.com
Assuming that the Bricklink data are complete and correct, there are 41 double sided heads without a known release date, and the trend seems to have started in 2001 with this one:
I was a child with wealthy parents during the early 90's and thus own almost every set released during that period. apart from the harry potter one mentioned, the first that showed the same face with different emotion I remember getting was a small set that included a new skeleton face as well as a mummy. This Mummy was double sided with one face asleep, and one face awake.