Steel is by far the most often picked material for garage doors. They aren't terribly expensive, they're quite durable and require very little maintenance, and they can come in pretty much any style you might demand. Steel's appearance is flexible, as it can be painted or formed into panels, and can be treated with a substance that makes it LOOK similar to wood. Though the mimicry isn't perfect.
When you're actually doing your shopping there are a few things to keep in mind about steel: it's a pretty ineffective insulator, and probably requires an outside source of insulation to keep your garage habitable and save you energy. Also, steel panels tend to vary in their thickness, usually varying with the price, and if you want a steel door that will withstand basketball games, you'll have to pay for it.
Aluminum doors are similar to steel in many ways, especially in that they have faux wood texture options, and various finishes and paints to change their appearance. They are on the whole much less heavy than steel, and usually cheaper, but they're even more likely to dent. Again- if you're not hosting basketball games in front of your garage door, or have kids that like to play handball, you'll probably be fine going for the cheaper, thin aluminum garage doors.
Ask a garage door installation expert about which metallic material is right for you.