http://stackoverflow.com/questions/18939421/what-should-xcode-6-gitignore-file-include#
new
Another answer is that there's a website called gitignore.io , which generates the files based on the .gitignore templates from https://github.com/github/gitignore.
old
The easiest answer is that mine looks like this:
# Xcode
.DS_Store
build/
.pbxuser
!default.pbxuser
.mode1v3
!default.mode1v3
.mode2v3
!default.mode2v3
.perspectivev3
!default.perspectivev3
.xcworkspace
!default.xcworkspace
xcuserdata
profile
.moved-aside
DerivedData
.idea/
# Pods - for those of you who use CocoaPods
Pods
which I believe is the same .gitignore that GitHub sets up with all their repositories by default.