Sin City and the Crow for me as well. I've also seen Road to Perdition which is great. A History of Violence, LXG and From Hell without reading the source material. I read V for Vendetta way back in 1994. My boss had the book. I think Sin City is the best of the ones I've seen.
Sin City, V for Vendetta and Road to Perdition I hadn't read any of those comics until after the film came out, I did not even know that they would of been any good until watching it at my local theater.
First, a question just to be specific - do you mean only the ones, the source material of which you actually will never read (or at least don’t plan to), or the ones that actually got you in reading their source material later on also count?
Well anyways, the only ones that got me so impressed that I actually feel worthy of mentioning are Sin City (I got all of the books after I saw it) and A History of Violence (never even heard it was based on a comic till recently).
There are of course several others but they didn’t impress me that much like those two did.
Those count. I saw "Sin City" & subsequently read "The Hard Goodbye", since it came w/the DVD. I plan on reading V when my comic shop gets some more copies in. It seems to be in high demand for some odd reason.