Can you recommend a pregnancy workout routine?

Hi all,
I am in the normal weight range (142, 5' 5") and was working out regularly for about 8 weeks before my little surprise. I would like to maintain some level of fitness to feel good and keep weight gain reasonable. I am 5 weeks along with #4.

Can you recommend routines, maybe by trimester? Are there DVDs I can get? Any help would be appreciated...I am already tired and nauseous but knowing what to do with regard to exercise will help. I am a yoga person so I plan to do that, but I'd like to do strength and cardio as well.

Thanks!