My wife and I have a 1.5 year old daughter. We were married when we were juniors in college. When we found out my wife was pregnant, I had graduated college only one month earlier, and had just bought a house in the town where I had found a job. Needless to say, we had a whole new world of expenses come crashing down on us that we might not have been the most prepared for. When we found out she was pregnant, we owed about $150,000 on the house, $40,000 on our combined student loans, and $28,000 on a car. I was the only one working at the time. (I'm an Electrical Engineer, so I probably make better money then most college grads) The added expense of a child was very nerve wracking.
Something to keep in mind, is how your health insurance works. Something that I didn't really think about was the deductable. We met the individual deductable on my wife very quickly, and I thought I was home free from there. Then we went to the hospital to have the baby. There we a bunch of hospital and baby related stuff that wasn't covered. Then I got hit with the fact that once the baby leaves the mother's womb, it is a new person with it's own deductable. I probably ended up spending somewhere around $2,000 just in the 3 to 4 days at the hospital.
Part of that $2000 is cafeteria meals for myself, since I stayed there the whole time with her. Something I really would suggest, it packing some diapers and various sizes of baby clothes. The hospital I stayed at charged you like $30 for a diaper! Those things add up fast. You end up getting nickeled and dimed to death at the hospital.
Also, start looking for baby stuff that you need now. You can find great deals on cribs, baby clothes, toys, etc at garage sales or craigslist or even consignment sales. Don't be tempted to do like my wife and buy fancy stuff for the baby. Babies are messy, and they will destroy things. They also grow quickly, so don't be afraid to buy things that a cheap and plastic if you must buy them new. It really helped me to spread all those expenses out over the nine months of pregnancy instead of having to buy them all at the last minute.
My wife is working now too, because she just didn't like staying at home all day with the baby. (It was driving us both crazy!) If you end up not staying at home, make sure to look into a depended care flex plan to pay for daycare pretax. That has worked out really well for us. I live in central Nebraska, and pay $105 a week for daycare. I hear it is much higher in most places.
On a somewhat related side note, the baby is what got me most interested in personal finance and brought me to this site. I came here, because I looked at a 529 college plan and realized what it was going to cost me to send her to school. I'm trying to cut back on all our other expenses to save up properly. Luckily, I got a raise after my first year of about $300 a month, so I put it all into her college fund. If you are interested in 529 plans, I have mine here: http://www.planforcollegenow.com/ (it's for Nebraska, but they have some nice calculators, etc)