The NXP LPC1342 microcontrollers have a built-in bootloader which allows programming the device via usb: The bootloader is triggered by pulling one pin to GND on bootup. The microcontroller then enumerates as a USB mass storage device onto which the firmware file can be copied without any additional hardware or drivers with most operating systems.
Apparently there are other devices which have unusual methods of in system programming (i.e. not via a classic serial interfaces SPI, JTAG, SWD, etc).
Does anybody know other examples of devices programmable from factory in system by USB, ethernet or similar?