I should clarify that the bittering hops I like using for lagers are not substitute for noble hops, but the slight flavors they impart (used as bittering hops) complement the noble hops flavor. As Jeff points out, Clusters works well in a CAP, especially if you finish it off with Saaz. Its also good in other pilsner styles = Pilsner Urquell uses Clusters as a bittering hop.
Perle I think of as being somewhat minty, Northern Brewer as earthy, and Styrian Goldings also with a blackcurrant note. They all seem to compliment noble hops in lagers. I used to use Magnum quite a bit, it almost seems a little too clean (kind of like eating walleyes, I prefer eating fish that tastes like fish).