It actually depends on the anime for me though, some of the dubs are pretty decent, yet some are not as quite. Red Garden for example, their singing scene in the Japanese version was quite decent and felt, yet... let's just say that the english version butchered it XD
But, here's an example of a decent Dub, though the story was changed around a little, it's quite funny:
Ghost Stories, Episode 4 Dub
http://www.veoh.com/videos/v6928657d3yTntz8
Unfortunately, I can't find the sub, but it's less funnier than this.