Linux kernel documentation
[http://lxr.linux.no/#linux/Documentation/usb/:Documentation/usb]
[http://lwn.net/Kernel/LDD3/:Linux Device Drivers] - Read Chapter 13 on USB
USB intro
[http://www.beyondlogic.org/usbnutshell/usb1.shtml:USB in a nutshell] - A somewhat dated, but short overview of the USB 2.0 specification
[http://www.usb.org/developers/docs/:USB specifications] - official specifications from the USB-IF
Talks on USB
"Superspeed Me: USB 3.0 for Linux" - [http://mirror.linux.org.au/linux.conf.au/2010/friday/50230.ogv:video] (2010)
"USB port power off Kernel/Userspace API" - [http://linuxplumbers.ubicast.tv/videos/usb-port-power-off-kerneluserspace-api/:video], [http://dl.dropbox.com/u/96820575/sarah-sharp-lpt-port-power-off2-mini.pdf:slides]
"Vampire Mice: How USB Power Management impacts you" - [http://mirror.linux.org.au/linux.conf.au/2013/ogv/Vampire_Mice_How_USB_PM_impacts_you.ogv:video], [http://www.slideshare.net/saharabeara/sarah-sharpvampiremice201301:slides] (2013)