USB

• USB HOWTO
  linux-USB
  linux-hotplug.sourceforge.net
  list of devices
  usb.org
  book
  book USB Complete Second Edition
  USB Central
  links on Google directory
  3G USB modems and cards (i.e. http://wiki.debian.org/Usb_modem)

USB driver development

• linux-usb-devel mailing list
  a USB chip