There are simply too many great things to choose from at Siggraph 2010 and every day is a struggle to narrow it down to only one track at a time.
For instance tomorrow there is a two part course with the title "Advances in Real-Time Rendering in 3D Graphics and games" that covers the entire day. Then there are interesting paper presentations in Boundaries, Edges and Gradients from 9:00-10:30 as well as the Mesh Colors paper in the Textures session and Video tapestries with continuous temporal zoom paper in the Video session both at 10:45-12:15.
There's also a few interesting talks by NVidia tomorrow which you can find more info on here. It could be interesting to go to the NSight talk 11:00-12:00 to hear a little about what it brings to the GPU programming scene.
At 17:15 there is OpenGL Birds of a feather by Khronos at the Wilshire Grand Hotel you can register here.
Since the paper presentations can be streamed from the ACM digital library after the conference I will probably stick with the course or maybe I will head for a day at the Geek Bar to be able to browse a little of it all.
Look forward to yet another great day at Siggraph