Hardwood KNOTTY ALDER is a furniture grade lumber that is commonly seen in doors and cabinets - Clear Alder (no knots) is also available (typically adds $50-$100 per shelf/mantel). Both types can have varying amounts of texture added or be completely smooth. Most of the work on my site is made with Alder with a distressed finish.
WHITE OAK is another popular option, especially in flooring now days. Certain stains tend to accentuate the grain than others - natural with a clear varnish is the most popular option. Mid tier pricing, will add $100-300 per shelf/mantel, depending on the overall size.
Maple is the standard for high quality cabinets but also works well for floating shelves and some furniture when a smooth finish is desired. Maple has a light wispy grain and lighter coloring that shifts any stains to the lighter end. It works really well for grey tones and when you want to minimize red tones. Mid tier pricing and adds $100-$200 per item.
Walnut Everyone loves walnut, but it is one of the most expensive North American lumbers commonly available. It has beautiful dark grain, very durable, and has gorgeous coloring. It's almost worth it. ha! Typically adds about $200-$400 per item.
Cherry has beautiful grain, and used to be the standard for custom furniture but went out of style because of the typical reddish color. New stain and varnish options can give it an updated look. Beautiful, medium tone, smooth grain, and priced between oak/maple and walnut. Here is a cherry mantel with just a clear varnish.