Big party member scoffing notwithstanding (sorry Ritter :-) ), if you dislike centrism, I think you could try the WASG wing of the forming new Left Party (Linke) too, and the Greens too.

The WASG is in part breakaway SPD, in part altermondialist and other new movements. (Its senior partner in formind Die Linke, the PDS, may be fringe in NRW, but not in the East.) From residual symphaties from my time in Germany (tough not NRW - I was in Hessen) and my high regard for their work in government, I'll put my first recommendation behind the Greens.

_{*Lunatic*, n.
One whose delusions are out of fashion.}