Hogwarts Idol
It's actually part 3 of it, but this is by far the best part of it. Snape's part is the last, so if you only care about Snape, you could just skip to 3:21
But you still should watch the whole thing, because it's just plain awesome. When it gets to Snape and Voldemort's song, it's the kind of thing where it's pretty funny, but the pure epicness of it keeps you from laughing. I mean, the song totally fits them, and everything is timed perfectly. I've probably watched this over 20 times... Yeah, it's that awesome.