My mom used to listen to older glam-rock stuff ( think Alice Cooper, Billy Idol, Kiss, Queen, that sort of stuff ), rock ballads and some other classic rock. Also listenst to other '70s and '80s (synth)pop/new wave stuff like Depeche Mode, Madonna, Nena, a-ha etc. Nowadays she doesn't really listen to music all that much unless the radio happens to be on. She did at some point like Within Temptation and Evanescence enough to buy a live dvd of theirs though..
My dad listens to a whole bunch of stuff.. Off the top of my head I know he nowadays digs Bob Marley, The Beatles, David Bowie, The Smiths, Pink Floyd, Simply Red, The Doors and a bunch of Dutch shit I hate. I guess he's more open-minded than my mom when it comes to music, he actually listens to stuff if I recommend it to him.