RDEGRAAF.nl [Homepage of Rob de Graaf] has a fascinating collection of mathematics. Found Roger Penrose's online lectures on twistor theory (they're actually hosted by the Isaac Newton Institute here) through this site. Absolutely knocked out by the Penrose drawings. Managed to stay with it just about long enough to understand the motivation behind transforming things into twistor space. Those diagrams are wonderful though. Here's a little web quest for you - try to find Penrose's depiction of Schrodinger's cat.