We chose our Beagle last summer from the shelter, and it was a great option. I don't think I'd ever consider getting a pet anywhere except from the shelter in the future. First, we were saving an animal who otherwise would've been killed. Second, it was a great bargain: We paid $75 for him, which included his rabies and puppy shots, and we were given a certificate to take him to the spay/neuter clinic within 30 days and have him "fixed" for free. (Definitely spay /neuter your dog -- it's simply the responsible thing to do.)
Another option: Look into fostering dogs. This gives you a chance to "try before you buy".
I'll second what another poster said: Don't hurry. Adopting a dog is a commitment, and you want the right dog -- not a right now dog.
One health comment: I told the kids that we were taking him THAT DAY to the vet to make sure he didn't have heartworms. Heartworms are extremely expensive to treat, and the dog doesn't always survive. If I were already attached to the dog, I would pay for his treatment . . . but I wasn't willing to take on a brand-new dog that already had the problem. If you choose a young dog, your chance of heartworms is smaller.
From a frugal point of view, I've been very happy having chosen a Beagle: He's 20 lbs, which is a nice size for an indoor dog; a small dog doesn't eat much and his collar, bed, medicines, etc. are cheaper. One small negative: His stomach is a little delicate, and he can't eat cheap food; I'm paying about $15/month for his food. His short hair is easy to wash at home, and he doesn't require grooming (except trimming his nails). I set out looking for a Dauschund, but quickly ran into Beagles and haven't been disappointed in the least. We had a Cairn Terrier when I was a kid, and that was also high on my list of possibilities. I think I would like a Yorkie or a Shih Tzu, but I wouldn't like keeping up with the brushing and grooming.
I'll echo someone else's comment: Obedience classes were well worth the cost. He's my first indoor dog since childhood, and both he and I learned in the class.
As for boarding, I suggest you find a friend with a similar-sized dog and agree to "trade" boarding when one of you goes out of town. FREE, except that you might give the friend a box of chocolates or another small gift as a thank you.
Finally, I would be a bit concerned about getting a dog while you're planning for a baby. A baby is such a huge time commitment and a lifestyle change. You can always adopt a dog later. A dog with a newborn may not be such a big deal . . . but a toddler is going to pester a dog, pull his tail, get into his food dish, and so forth. Choose your breed with toddlers in mind. If you wait, I think children are really ready for a dog around the time they start school.