This year's Serpentine Pavilion by Sou Fujimoto is great. Although of the ones I've been to, this is still my fave. Go and have a look if you're in town; the last day is October 20.
My heart melts every time I see this picture. I've taken a series of pictures every time Oomoo gets his hair cut (by his dad). It'll be fun to look back at them in years to come!