In game advertisements:
In "Secret of Monkey Island" LucasArts put in an
advertisement for another of their games -- LOOM.
The way they did it was: In the SCUMM bar one of the
dudes at the bar has a little badge that says "Ask me
about LOOM". You walk up to him and one of the dialog
options is "So, tell me about LOOM." At which point
<ADVERTISEMENT> starts flashing on the screen
and the guy launches into a moderately silly sales pitch.
After it is completed, you have the opportunity to
ruthlessly mock him about it, then continue with the
rest of the game.
I thought it was well done.
Respectfully,
Brian P.