The most popular choice for a pitched roof is asphalt. Cheap, light and durable three-tab shingles are by far the most common roofing material in the U.S. They look fine on almost any home. They do not require structural reinforcement and they stand up to the weather in most areas. Specialized stain-resistant shingles are even available for humid or coastal areas.
The next step up, in cost, quality and appearance, is a laminated (or dimensional) asphalt shingle. These thicker shingles have a varied, three-dimensional appearance that resembles cedar or slate more than three-tab asphalt. Laminated asphalt is more expensive than traditional asphalt, but it also is rated to last longer.
On the other end of the asphalt spectrum, asphalt roll roofing is one of the cheapest options on the market. It is easy to install, and it may be a good temporary option if you must wait to install a permanent roof or are planning to "pop the top" and add a second story.