Many a time I want to see how the site I’m working on loads on a slower connection. A 20gb Fiber connection is not ‘real world.’
These are some Bandwidth Limiter, Bandwidth Throttle, Bandwidth Shaping apps that I’ve found. Slowly seemed to work the best and there’s a free version.
Entonnoir

http://tools.chocoflop.com/entonnoir_en.html
SPEEDLIMIT

Speedlimit is a prefpane
OSX Lion Network Link Conditioner

Comes free with Xcode Dev tools
https://developer.apple.com/technologies/tools/
Slowly

$4.99
Free for two speeds: 56k and LTE mobile network connection
http://slowyapp.com/