I install these on OS X every single time I set up a new one:
- Homebrew – package manager http://brew.sh/
- QuickRes – resolution manager http://quickresapp.com/
- ClipMenu - clipboard manager http://www.clipmenu.com/
- QuickCast – quick screencasts http://quickcast.io
- Honeycomb – desktop client for Foursquare https://itunes.apple.com/us/app/honeycomb/id905814675?mt=12
- SmoothMouse – Windows-like better mouse acceleration http://smoothmouse.com/