This journal is deprecated. All of the listed types of games can be run in ScummVM now.
First, Linux PC's:
Lucasarts games: http://www.scummvm.org/
AGI Sierra games (Lsl1, Sq1, Sq2, Kq1-3, etc): http://sarien.sourceforge.net/
SCI0 Sierra games (Sq3, Lsl2-3, Kq4): http://freesci.linuxgames.com/
SCI1 Sierra games (Sq4-5, Lsl5-6, Kq5, etc) and oddballs like willy beamish and all those old games like tunnels of armageddon: http://dosbox.sourceforge.net/
Windows Sierra games (Sq6, Lsl7, etc): http://www.transgaming.com/ (or apt-get install wine)
Any platform, Sierra games: This guy has done the unpossible, writing timing fix patches for the games so you don't have to kludge them with slowdown utils: http://geocities.com/belzorash/
LucasArts games: http://www.scummvm.org/
AGI Sierra games: http://www.agidev.com/nagi.html
SCI Sierra games: http://sourceforge.net/projects/vdmsound/
Games that just don't work right:
And just for grins, because it's freaking awesome:
Good luck, let me know if you have any problems.