C-Notes and Benjamins are slang terms for which denomination of U.S. Currency?

C-Notes and Benjamins are American $100 bills

https://en.wikipedia.org/wiki/United_States_one_hundred-dollar_bill
Find it under "Nicknames"

The $100 bill has many nicknames including:

C-B, C-note, from the Roman numeral C for 100, and B for Bill;
Benjamins, Benjis, Franklin, Frank, Benjy, Ben, or Benny because of Benjamin Franklin's portrait;
Big one, refers to the largest denomination currently in use;
100 Bones, 100 Clams refers to the $1 bill multiplied by 100.

[Text added -- Zb]

One hundred dollar bills are sometimes called "Benjamins" (in reference to their portrait of Benjamin Franklin) or C-Notes (the letter "C" stands for the Roman Numeral 100).

http://www.answers.com/topic/federal-reserve-note-1