A few years ago I lent a friend 'The Spanish Prisoner'. He loved it and said "It was the best film he'd never heard of" which I thought was a great line.
I think I agree with him because I bought the film with nothing to go on. I was browsing a sale on a Region 1 site and the overview intrigued me and that Steve Martin was playing a straight role. At the time, David Mamet meant nothing to me (now I look out for work he's associated with) and apart from Ben Gazrra there were no other cast that I recognised. I hadn't seen any reviews and no-one had mentioned it to me even in passing. I couldn't have bought a more blind title and I really liked it.
The Station Agent would be the next one. Marvellous film, bought blind again. However, I was vaguely aware of it through reviews. Then there are the Fox Film Noir releases. Despite knowing they were being released, I committed to buying them on the basis I recognised very few of them. Boomerang was the most expensive DVD I ever bought if you adjust for content versus value, but I hadn't heard of it and it's fantastic. House of Strangers, No Way Out and Shock stand out as real favourites now as well.
Pete reminded me of this rare situation in his classics marathon. He's apparently really struggled to even identify a couple of the titles! There could be a real gem buried in there.
So what are your favourite films, that you'd never heard of?