Running and Pregnancy

Since I have become pregnant, exercise has become increasingly more important to me.  Certainly exercising was important to me before, but now it has become a gift I can give to my baby as well.  Keeping Mommy healthy means the baby is more likely to be healthy and I take this truth very seriously. 
However, not so long ago, many doctors did not recommend exercise for pregnant women.  Certainly a brisk walk was encouraged, but keeping your heart rate at an optimal level was always a concern.  However, opinions on this have now started to change, and exercise is seen as a crucial part of pregnancy.  To find more information on this topic, I borrowed the book Runner's World Guide to Running and Pregnancy from the library. 
This book gives great information and advice as to how to run during pregnancy, where your heart rate should be, how your body will most likely react to running during the different trimesters of pregnancy, and personal testimonies to how mom's stayed in shape while pregnant.  If you are a runner and are wanting to have children soon, I would highly recommend reading this book. 
Now, I would not consider myself to be a runner.  I run, but I do not identify myself as a runner.  In fact, I have personally decided not to run during pregnancy, but have been interspersing stationary biking, pilates, yoga, and walking 5-6 days a week, 30-60 minutes a day.  My goal is always 6 days a week, but my pregnancy napping (non)schedule sometimes precludes me from getting my exercise in for the day.  However, this book still gave me great information on cross-training and the overall effects of exercise on pregnancy. 
My decision to discontinue running stems from the wish to preserve my joints, and that I was not where I wanted to be fitness-wise when I became pregnant to maintain running the three-miles I had built up to over the course of the summer.  If I had perhaps been able to complete a good five mile run in an average amount of time, then I would feel comfortable doing 2-3 miles at a slow pace while pregnant.  Another goal for another baby, perhaps?   
I have not foregone running altogether, however.  Indeed, I am cross-training throughout this pregnancy so that when I am ready to go back out there to run after the baby is born, I won't be starting from scratch. 

During pregnancy, doctors do not advise losing weight.  Since I am still not at a healthy weight for my height (although I am 7 pounds lighter than I started a while back), my goal is to maintain my weight for as long as possible.  I will gain weight during this pregnancy- anything less than 15 pounds would be very inadvisable- but exercise will keep me on a path that will be allow me to gain the weight necessary in a healthy manner.  My diet has also been mostly good (another post of another day).  So with these combine efforts, my hope is that after the baby is born, with the help of breastfeeding, the excess pounds will just melt away.
Are there any books that you have read that have encouraged you to keep exercising, pregnant or not?  Feel free to post any advice you might have regarding exercise and pregnancy.