I used to play a lot of adventures in my pre-Doom gaming days... and my all time favorites are Indiana Jones and the Fate of Atlantis, and Maniac Mansion 2: Day of the Tentacle.
With Indiana Jones 4 due out the summer of 2006, I wouldn't be surprised if LucasArts is planning another IJ adventure to coincide with the movie's release. Think about it... none of the S&M staff were axed, 2 years is just about right to create a polished adventure, and an IJ adventure would be a sure-fire hit, thus less of a gamble than S&M. I know... just wishfull thinking.