This is what is in my Global .gitignore file which you can see as a gist on GitHub, but the Xcode list can be applied to other systems
# Mac OS X
*.DS_Store
# Xcode
*.pbxuser
*.mode1v3
*.mode2v3
*.perspectivev3
*.xcuserstate
project.xcworkspace/
xcuserdata/
# Generated files
*.o
*.pyc
#Python modules
MANIFEST
dist/
build/
# Backup files
*~.nib
\#*#
.#*