DS, 3, loves my old duplo from when I was little, and last Christmas we got him some more from eBay - the stuff on eBay is so much more fun than the new sets! I just had a little look at what there is now and I've got about £150 worth on my Watch list!
He does love his duplo, but I think I might love it just as much. My budget is only £20 so I'm recommending it to everyone else so I can enjoy it vicariously!