Our friends at VR zone mentioned R680 but our sources close to ATI confirmed that there is no such card. ATI did make some presentation to catch who is leaking the info, mentioning false chips including the R650, R670 and now even R680, just to catch who is leaking the stuff.
Someone was telling things to Nvidia and Intel, among others and the company was not that happy about it.
We can confirm the existence of RV635 as a 55 nanometre shrink of RV630, but not the other chips. You can read the original post here.