Satan and Tokolosh - great pics there. I've seen some of yer actualy Bridget Riley art, at that humongous gallery in Buenos Aires (bugger, cant remember the name of it offhand), and I remember being well impressed by both the scale and effect of her pieces - she sure likes to work with big canvases. One day, I will see "Guernica" as well.
I'm a fan of 20's Weimar-era genius Georg Grosz, and I was knocked away by this painting the first time I went to Berlin:
("Metropolis")