Brand name is definitely the way to go – not necessarily for quality of product, but for the availability of information and informed help that goes along with it. If your hardware store offers "Grandma Margies's Generic Housepaint," avoid it, no matter how cute the cartoon granny on the label is. The price range for brand-name DIY interior housepaint is around $17-$25/gallon. Outside of that, in either direction, and you’ll be wasting your money.

You can buy your paint at Home Depot or a hardware store, but paint stores have the benefit of specializing in their product. The folks at, say, a Benjamin Moore-branded paint store will not only know their products inside and out, and be able to tell you which work together, but they’ll also know a lot about painting itself. They're great for getting tips, and their prices shouldn't run more than a buck or two more than Home Depot generica.

Color me indecisive
As for picking a color, raid the paint counter for inspiration. Grab all the paint samples you can carry home with you, and tape them, a few at a time, to the wall. This gives you a chance to see the color according to the light it will actually be under, not those awful store fluorescents. Take your paint chips and tape them to the wall a few at a time. Give 'em a good look when you walk by at random hours - daylight, lamps, whatever lighting situations they'll be dealing with. Start eliminating them a few at a time....It's Paint Chip Thunderdome!