I love the original watchtower, about the same amount as I love the Hendrix verison, they are both saying something different;y. I think it is worthy of note that ever since the Hendrix cover, Dylan says that he performs Watchtower as a tribute to him, Dylan does watchtower now the way Hendrix did.
I cannot stand Leonard Cohen, except in very rare circumstances, but he writes great songs, so covers seem to work if done properly, like Buckley's.
I have a fairly varied music taste, I didn't even mention all the jazz tunes that I love, I was sticking more to rock on that list, or I could list another 101.
Not surprised you didn't like the Madonna, I wasn't expecting a hellavu lot of people on this site to agree with me.