Before you decide on a breed, you probably want to read this:
Are you ready for a dog?
http://dogbreedinfo.com/ready.htm
The first time ratbastid and I looked for a puppy, we went to the pound, had one all picked out, and had scheduled the adoption. We bought a book on raising a puppy and promptly realized that there was no way we could keep a dog. We lived in a tiny apartment, and I was a grad student. The puppy we'd fallen in love with was going to grow up into a beast of a chocolate lab, who would need lots of attention, training and exercise that we didn't have the time to provide. It wouldn't be fair to the dog, and we didn't have the money to pay if she ripped the apartment apart out of boredom and frustration while we were at work/school.
So: proceed with utmost caution and honesty with yourself. You will be utterly responsible for this little pet's well-being and happiness...do you have the time, energy, money, and interest to do what it takes to have a happy dog? You might want to find a friend with a dog and "puppysit" for a weekend to see what's involved. Also, think hard about whether you want a puppy or an older dog. Having gone through both, I highly recommend getting an older puppy or adult dog who's already been housebroken and crate trained, as long as you know their temperament (see below) and that they've been well socialized to humans and other dogs. Puppies are adorable, and they are more likely to form strong attachments, but they are a PAIN IN THE ASS, no question.
If you decide you are ready for a dog, do some serious research on breeds.
www.dogbreedinfo.com has good information on breed temperaments and health (see
http://dogbreedinfo.com/pembrokecorgi.htm and
http://dogbreedinfo.com/cardigancorgi.htm. You could also look at a "pet selector" like
http://dogbreedinfo.com/search.htm
or
http://selectsmart.com/dog/
that will ask you questions about your lifestyle and what you're looking for in a dog, and return lists of dogs that will suit you.
You should also look into temperament testing to see how the animal reacts to certain behavioral challenges. This will help predict how the animal is going to behave once you adopt it. It'll help weed out aggressive or destructive dogs.
http://www.paw-rescue.org/PAW/PETTIP...emperament.php
If you're getting a pure-breed, go to a reputable breeder and not to a pet store. If you're going with a rescue/shelter dog, be sure they have some kind of "return policy" if the dog doesn't work out.
Getting a dog is a big responsibility. Do your research first and be thoroughly honest with yourself about whether you are ready for it.