USB Parasitic Power

TPS2550 and TPS2551 power distribution switches have integrated FETs that support a 100-mA to 1.1-A current limit range for a standard USB port or other applications requiring a current limited switch

.. TPS2149 USB power controller device.. TPS2114 TPS2015

TI presentation:

Micrel MIC2505 etc

Arduino Duemilanove uses POLYFUSE..

Another: Raychem MINISMD050-2 in MINISMD pkg