I just found out about Alice and Scratch. I will be implementing those pretty soon. But, I wonder, what would be good material for kids from 1st grade thru 4th/5th?
Toontalk is something to look at. I used it successfully with group of ten- to eleven-year-old children, and it's been used with much younger kids. Of course, I think Scratch has too. But Toontalk is specifically built to feel more like a game. It's essentially a 3D world that kids can explore and interact with, and in which they create programs by training robots. Highly recommended.
The Toontalk 3d environment ingeniously operates as a metaphor for sophisticated programming concepts. There are quite a few academic papers linked on Toontalk site about the educational theory behind Toontalk. Here's one interesting paper that describes how the Toontalk 3d objects map onto abstract programmming concepts.