I dont have all, but from the bundles I have these are native 64bit executables:
- Anomaly
- Avadon: The Black Fortress
- BIT.TRIP BEAT
- BIT.TRIP RUNNER
- Braid
- Cogs
- Dustforce
- EDGE
- Eufloria HD
- Fieldrunners
- Gratuitous Space Battles
- Jamestown
- Osmos
- Rochard
- Spirits
- Splice
- Super Meat Boy
- Swords & Soldiers HD
- Uplink
- Wizorb
- World Of Goo
- Zen Bound 2
Bundles:
- Humble Bundle for Android 3
- Humble Bundle for Android 4
- Humble Indie Bundle 6
- Humble Indie Bundle V
/edit:
That's 22 of 35 (with 2 being wine wrapped and one is a flash game)
Dungeon Defenders is 32 bit.
The Binding of Isaac has a .tar.gz download, a 32 bit deb and flash download so I guess all is 32 bit.
No idea about closure, it's .sh installer, could include 64 bit or not.
Legend of Grimrock is 64 bit for me, I guess the installer has a 32 bit version included ("Supported CPU Arch's x86, x86_64").
For Snapshot you can choose between 32 and 64 bit.