The first chord of Beethoven's first Symphony in C is a seventh chord. It's actually the chord of C which is the key of the piece, but because it's a 7th it's unstable and has to resolve to F. Not C! Not only that but the strings are played pizzicato. The work is unmistakable from the very first note. Even in his first major orchestral statement he's approaching an original and revolutionary stance. This was not the first time a dominant 7th chord opened a symphony but it was still a pretty cheeky move for a relatively unknown composer. Funnily enough, around this time a review of B's Clarinet trio in the AMZ music review said that he could never hope to become famous unless he tried to "write more naturally" (Burk).
Here's a great Paavo Jaarvi performance of Beethoven's 1st: