Apache
Bandwidth-limiting Sites
See https://svn.apache.org/repos/asf/httpd/sandbox/mod_bw/mod_bw.txt for more information, but after installing the mod_bw module using, e.g., apt-get install libapache2-mod-bw && a2enmod bw, the following directives can be added to a virtual host's declaration to limit the per-user bandwidth to 56kbps:
BandWidthModule On ForceBandWidthModule On BandWidth all 56000 MinBandWidth all -1