I found this video on the official It's Always Sunny blog. The Nightman Cometh, which was the final episode of the season, is hilarious and should be watched in it's entirety (especially Charlie's proposal). This is a behind the scences video and includes a song that I think they were wise to cut. It isn't on the same level as the songs that made it into the episode, which I thought were genuinely good "musical theater" songs. The ending is pretty funny though.