Covers rock!!! I'd like to see songs with a male voice covered by a female and songs with a female voice covered by a male.
I wouldn't say that covers 'rock!!!' per se, but there's often something
interesting about them in a purely aesthetic way. Why did the singer/band cover this particular song? What did they change about it to suit their own musical tastes/abilities? Is it merely derivative or has there been some genuine improvement?
Genuine improvements upon originals are rare; conversely, derivative adaptations are common, leading people seek out proverbial diamonds in the rough. Obvious ways of differentiation include switching up the sex of the vocals, slowing the melody down/speeding it up, changing the key, revamping all the instruments to blend genres. The best covers end up doing at least
some of all of this, developing work of artistic merit rather than free riding upon the successes of others.
Two covers that I really like at the moment are both by Adele: 'Make You Feel My Love', originally by Bob Dylan, and 'Lovesong', originally by The Cure (of which I seem to be the only person that likes it). At times, it genuinely feels less like you're listening to a 'cover version' of a song' instead, it seems like you're almost discovering new stuff you've never heard of before.
Also, I'm surprised no one's mentioned what
Glee has done for the permissibility of the cover version. A lot of their stuff I really don't like (mainly to drown everything out either in AutoTune or bland group vocals), but when they get their songs right, they often work wonders. (See: 'Maybe This Time', Journey medley, the whole episode entitled 'Duets')