Foo Fighers write some very good music, and most of it is very simple too. Go for it, you could learn a much more technial song if you wanted, but start slow so you can learn more and not be thrown off when you can't get a riff down. Easy songs for rock... lets see.... try some AC/DC tunes, Boston has easy stuff. I could go on, but your best bet is to take your favorite bands and learn their riffs/songs. My best advice, when learning a new song, if its going harder tha it seems, look at what chord shapes go with the notes, that way you'll have a better placing for your fingers and you'll move around more effeciently and smoother.