It gets really old having to create a site-specific .gitignore anytime I start a new project. It's especially troublesome since I tend to access the same repository when it's mounted on different filesystems, creating all sorts of superfluous, useless files (I'm talking about you, .DS_Store). Luckily, gitignore.io has your back, and can quickly generate lists of ignorable files from many different operating systems, editors, and programming languages. Very useful!
OSX .gitignore
### OSX ###
.DS_Store
.AppleDouble
.LSOverride
# Icon must end with two \r
Icon
# Thumbnails
._*
# Files that might appear in the root of a volume
.DocumentRevisions-V100
.fseventsd
.Spotlight-V100
.TemporaryItems
.Trashes
.VolumeIcon.icns
# Directories potentially created on remote AFP share
.AppleDB
.AppleDesktop
Network Trash Folder
Temporary Items
.apdisk