USBasp is a USB in-circuit programmer for Atmel AVR controllers. It simply consists of an ATMega48 or an ATMega8 and a couple of passive components. The programmer uses a firmware-only USB driver, no special USB controller is needed.
Features

• Works under multiple platforms. Linux, Mac OS X and Windows are tested.
• No special controllers or smd components are needed.
• Programming speed is up to 5kBytes/sec.
• SCK option to support targets with low clock speed (< 1,5MHz).
• Planned: serial interface to target (e.g. for debugging).

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AVRUSBBoot is a bootloader for the Atmel AVR controllers. It uses a firmware-only USB driver to transfer binary data from the PC to the flash of the controller. Once the AVR is flashed with the bootloader, no other ISP programmer is needed; then the microcontroller can be reprogrammed over USB.
Features

• Software works under multiple platforms. Linux, Mac OS X and Windows are tested.
• Tested with ATMega8-16
• No special USB controllers or smd components are needed.
• Bootloader fits into 1024 word bootloader block

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USB power bus is a great source for charging a single-cell Lithium-Ion battery. This circuit shown you how to build a USB-powered single-cell Li-Ion battery charger using National Semiconductor s LM3622 Li-Ion Battery Charger Controller.The battery-charger circuit is designed to operate as a high power USB function. To be compliant with USB Specifications (Rev. 1.1), a high-power function must not draw more than 500 mA from the bus during normal operation. The LM3622 uses the 0.25 current-limit resistor R1 to set a 400 mA maximum charging current. This leaves a 100 mA surplus that can be used to supply USB control circuitry and other functions in the device.source

The USocket – USB controlled Socket with PIC18F4550 designed by fvicente.The idea of this project is to control (switch off/on) two power sockets with a computer by using its USB port.It is a nice example to adapt this project to control other devices with USB port such as LCD ,stepping motor etc.This project no extra power supply required.It use the power from USB port.The project come with nice documented including PCB and firmware.source

An alternative controller for the Pinch Glove fingertip contact glove. Something as futuristic as a data glove should connect through USB, not RS232 as in the original design.This device fits into a very small SubD adapter housing, consumes low power (max. 20 mA), supports USB standby.source