The Null Device
A big list of useful shell commands for OSX. Some of these are generic UNIX shell tricks, but many are OSX-specific and quite useful; to wit, a few examples:
# Copy output of command to clipboard
grep 'search term' largeFile.txt | pbcopy
# display a Quick Look preview of a file; ctrl+C to kill
qlmanage -p photo.jpg
# converting an aiff file to 160kbps AAC:
afconvert track.aiff -o track.m4a -q 127 -b 160000 -f 'm4af' -d 'aac '