On the whole, I'm opposed to homework below 4th grade, with a few exceptions. Children should be reading for pleasure every day, which is a form of homework. Children need lots of practice in gaining math mastery, so a few math problems in an area they've already mastered are useful.
Sarah Bennett's Stop Homework blog has a lot of resources for parents. There's an interview with her at Stan Goldberg's Senior Dad (there are a lot of good resources there).
Recently, she wrote
I just watched the DVD of the Fall, 2008, Stressed Out Students conference, with keynote speeches by David Elkind, author of The Hurried Child and The Power of Play, Dr. Ken Ginsburg, author of A Parent’s Guide to Building Resilience in Children and Teens, Dr. Madeline Levine, author of The Price of Privilege, and Denise Clark Pope, author of Doing School. There are also 3 student speakers–2 highschoolers, and one college sophomore.
Here is the order form for the DVD: Download SOS_Stressed_Out_Students_DVD-order.pdf. It's $4.00 and would make a wonderful addition to a school library or as the starting point for a parents' group discussion about school stress.