trickle is a portable lightweight userspace bandwidth shaper. It can run in collaborative mode (together with trickled) or in stand alone mode.

trickle works by taking advantage of the unix loader preloading. Essentially it provides, to the application, a new version of the functionality that is required to send and receive data through sockets. It then limits traffic based on delaying the sending and receiving of data over a socket. trickle runs entirely in userspace and does not require root privileges.

[ http://monkey.org/~marius/pages/?page=trickle ]

To run trickle without the daemon and limit your wget download speed:
trickle -d 30 -u 10 wget <file address>

Or you could ask trickle to run an application with speed limit, ie, trickle -d 20 -u 10 firefox

Speed limit with a download speed (-d 20) 20 doesn’t necessarilly mean it will limit itself to download everything at 20kb/s but rather the average download speed will be 20kb/s.