Any good "windowed" games?

Any Turn-Based game probably.

Minesweeper and solitaire

Edit: uh oh and mah jong

Hearthstone

binding of issaac

One Way Heroics

Defense Grid

well.. mostly all of the games have window mode so u should be ok with most of all games

it is a blasphemy to play games and do other things in the same time!

Cookie Clicker

Luftrausers, FTL, Audiosurf, King Arthur's gold, Hammerwatch, Rust and i can't think of anything else.

Binding of isaac is a good one

Hearthstone if you like Card Games,
Kingdom Rush if you like Tower Defense,
FTL if you like strategy/micro management.

Fortix 1 & 2,
Sanctum TD (as you know),
Bejeweled 3,
Peggle Nights,
(most facebook games),
Avernum: Escape From the Pit (all spiderweb rpg games... There are around 10 of them),
The Cat Lady,
Obulis,
One Finger Death Punch,
Runespell: Overture,
Civ 5 (I think this one can be windowed and small),
Puzzle Quest,
Sword of the Stars: The Pit,
Tales of Maj'Eyal (TOME which you can get free if you don't want Steam version), The Walking Dead (Telltale story, not fps game),
4 Elements

I hope this helps out.

Kings of Chaos I guess? If thats still running.

I think that Neo scavenger might be good

long live the queen, don't starve

football manager

I like staring outside my window sometimes...

Organ Trial only plays windowed, and is a splendid game to play while doing other things.

I kept super hexagon open a lot while watching some livestreams. It's a fun little game that doesn't take a lot of time to play.

NightSky runs on windowed mode by default IIRC. And it's a nice little game to kill a bit of time on, when you don't have much to do. The later levels bit a little tricky, though, but other than that, it was fun

Plants vs. Zombies

how about real life? you can always watch other people playing through the window