https://docs.google.com/spreadsheet/ccc?key=0AmcTCtjBoRWUdHVRMHpqWUJValI1RlZiaEtCT1RrQmc#gid=0
And yes, the difficulty has dropped several times. It's even dropped multiple times in a row. You gotta remember: The price had risen to $31, and then crashed to $2. People were abandoning Bitcoin, and we lost almost half of the network. Everyone thought it was a fun little hobby that had run it's course and died. Well, everyone except those of us that believed in it, and kept mining.
For the difficulty beyond Aug2013, you may refer to the bottom part of this site.
http://bitcoinwisdom.com/bitcoin/difficulty