Yup, and several of them (although rather cheap) don't work very well (charge last much less than OEM). A couple seem to work ok.
I have had better luck buying rechargable Maha Powerex batteries 2700ah
from Thomas (I am sure others sell these also)
http://www.thomas-distributing.com/index.htmMore standard size i.e. AA AAA and the like than camera batteries
I have been (for my digital back at least) buying brand name lately. (occassionally Ebay has some listed But be sure it says brand name on them, they all claim to be Sony, Canon etc. but then it lists compatable)