What exercises are safe during pregnancy?

[Due December 20 2010!!!]

I'm already very overweight, and don't want to gain tons while pregnant. I think that if I stay as fit as I can during pregnancy it will help me to feel better about myself..even though I'm already big. I want an easier time to lose weight afterwards..haha! I plan on walking at least 5 times per week, but what other exercises are safe? Like, I would like to lose arm fat..would I use like 3-5 pound weights and do toning exercises, or leg lunges..anything like that?

Thanks!