Joe at 2011-04-06 11:46:55:
Total Recall (1990). The end makes it vague who exactly he is (or whether it's even all a dream) but a "mistaken identity" structure is certainly what drives the plot. The Bourne Identity uses a similar kind of structure -- the hero has mistaken *himself*.
I Am a Fugitve from a Chain Gang (1932). A sadly forgotten but powerful pre-code drama, in which Paul Muni's character is accidentally caught up in a robbery and mistaken as being one of the thieves and sent to a brutal prison camp, which he escapes.
Didn't that Depp/Jolie movie -- The Tourist -- also feature a "mistaken identity" plot? I didn't see it, though, so I could be mistaken.