Good games to play windowed?

i always play diablo 3 windowed while chatting or watching a vid. :3
tower defense games are also playable while doing something else.

I play alot of my games in windows mode while i watch tv programs, actually there are many that can be played windowed.
I suggest Hero Siege or Unepic.

I guess AdVenture Capitalist would be a good option.

I have a special category in my library for this kinda thing actually. I've got BoI as well, then GMod, Starbound, and Rogue Legacy. There are other games I've been wanting to use for this like FTL or XCOM, but I haven't gotten around to trying yet. Seems like they would work well enough.

Weird Worlds - Return to Infinite Space is a fun spaceship rogue-like that works well windowed.

Any grindy games like MOBAs, MMOs, looters would fill that role. As people said, Diablo is a good example, or Borderlands. Games that require about zero thinking and don't rely on twitch reflexes like console shooters, so you can do anything next to them.

LYNE. You play / watch a movie, and every now and then spend 1-2 minute on your current puzzle :)

HuniePop

Dofus used to be great :(

Other than Spelunky?
You can try Brogue - it's kinda cool.
Maybe try some turn-based RPG's? They usually don't require too much atention :)
One game that I always played in window mode (because it's was that small) was Bombie Zombie...
At the IE lessons in school I always played it - it's pretty simple, yet really fun. Try at least few seconds of it ;)

Anything turn-based, like Civilizations.

I usually use Hearthstone for this xD
That's a Blizzard card turn-based strategy, very interesting one.

For me it might be Faster Than Light. It's not so absorbing that I need to have it on full screen, so I check other things in the web from time to time* :P

*things like chatting on fb or browsing job offers, I never watch anything while playing - if I'm watching some movie or tv show I like to focus fully into it

Dark Souls

Solitaire.

Windosill

Nekopara- the window is half so you can hide it when anyone comes by to see what you're doing!