Throughput, latency, jitter, and packet loss can all impact user experience. Several software solutions that run on a host (or VM) allow these "levers" to be pulled.
Last time I researched I found a few possibilities:
Wanem
dummyet (link1)
dummynet (link2)
nistnet
shunra (link1)
shunra (link2)
tmnetsim
tmnetsim
Cisco WAN-Bridge (CCO Login Required)
If you want something client based maybe try shunra, and if you want something in the infrastructure wanem is pretty easy since their is a VMWare appliance available.