(Sorry, Jim, I know I didn't vote for ya on the Poll but I give credit where it's due anyway ...)
I'm just gonna say the same thing that Jim said. Buy from a local Paint Retailer. They're in the Yellow Pages under PAINT - RETAIL. You can buy your brushes and rollers there too. You'll need to measure the house before you go to get the right amount of paint. PREPARATION is the key. You want to paint a CLEAN, DRY surface and NOT in direct sunlight. As you transition from the 'end' of 1 can of same-color paint to another can of same-color paint, mix them with each other so they blend properly. Sometimes, and I mean sometimes, I've see where 1 can of paint (already painted on the house) ends, and another can of paint BEGINS! Blending prevents this problem.
Jim has made a great suggestion in that you should bring in pictures. Take one of each side of the house. I'd stick to light / neutral colors too. BUT, that may be dictated by the neighborhood, type of house, and your taste. If you have more ?'s, post up!