Identifying and dealing with counterfeit parts
Elliott Sound Products has an excellent writeup on counterfeit devices, including a lot of photographs of counterfeit devices next to the real version of the same device.

The page lists a significant number of previously counterfeited components, categorizing the vulnerable items as "any component that is priced higher than another of similar shape and size".  There are writeups for each of the following parts, mostly BJT power transistors:


MJ15003/4   
Sanken 2SA1216 (and the NPN type 2SC2922)
2SA1302 and 2SC3281 Toshiba 
OP-07 Opamps
2N2773 Power Transistors (probable)
NTE37 and NTE37 (probable)
LM3915 LED VU Meter
Toshiba 2SA1943 (and presumably 2SC5200)
2N3773
MJL21193/4 ON Semi MJL21193/4 (branded Motorola)
2SA1386 and 2SC3519 Sanken (branded IEC)
BU505 and MJE8502 ST and On-Semi


The author notes that the actual price of the counterfeit components is often insignificant, and that "loss of confidence, time, 'collateral damage', etc. are far worse"