After installing Snow Leopard and a few extra applications that I use daily, here is the breakdown of 64-bit vs. 32-bit applications.

Sadly, none of the third party applications are 64-bit yet. Luckily, Xcode 3.2 (included on the Snow Leopard install DVD) now defaults to generating universal binaries with the x86_64, i386 and ppc architectures enabled for Release builds, so we should be seeing a lot of third party 64-bit apps soon.

Apple 64-bit applications

Address Book Automator Calculator Chess Dashboard Dictionary Font Book Front Row Image Capture Mail Photo Booth Preview QuickTime Player Safari Stickies System Preferences TextEdit Time Machine iCal iChat iSync Xcode (and related developer apps) X11, Terminal and all other Utilities except Grapher, for some reason

Apple 32-bit applications

DVD Player iTunes Grapher (under Utilities)

Third-party 32-bit applications

Adium Adobe CS4 (all apps) EVE Online (cider) Git GoogleAppEngineLauncher MacIrssi Nambu Microsoft Remote Desktop Connection VLC VirtualBox

Notes

The list was generated by checking the application executables with the "file" command. E.g: 
iMac:Applications kennu$ file QuickTime\ Player.app/Contents/MacOS/QuickTime\ Player
QuickTime Player.app/Contents/MacOS/QuickTime Player: Mach-O universal binary with 2 architectures
QuickTime Player.app/Contents/MacOS/QuickTime Player (for architecture x86_64):    Mach-O 64-bit executable x86_64
QuickTime Player.app/Contents/MacOS/QuickTime Player (for architecture i386):    Mach-O executable i386