I personally dream of killing zombies or building turrets as the two games I usually play before I go to bed are Left 4 Dead
and Team Fortress
2. Once in a while, I do dream of killer mahjong tiles because I play the Shanghai tile game on Windows 7 in bed as well.
LucasArts has a game where you guide a girl named Sofi through her dream by placing random puzzle pieces for her to traverse. It's a little different in that you don't have control over her or what she does, kind of like Lemmings. Well, here's a look at the game in action if you're interested in something different from LucasArts.