Just running a few wget's should easily saturate your download bandwidth.
For upload, you might set up a web server on your computer (carefully poking a hole through your firewall for it), and then connect to a web proxy (there are a few of these that'll anonymise your data) and back to your web server. Then connect to your web server through the proxy and download (or upload!) a bunch of stuff.
It may be more effective to do these things one at a time, rather than both at the same time, as they may interfere with each other a bit.