Pine and Fir - popular and often found in older homes, they require more care to prevent scratches and indentations, but shows well if you desire a rustic or country look.
Birch - A softwood similar to pine. It tends to have more knotholes.
Oak - a durable hardwood, the most popular wood flooring. Accepts many stain colors, the most varied colorations available in wood flooring.
Maple - lighter colored with much less pronounced graining than oak.
Hickory and Pecan - very popular, often with strong variation in color in the same board.
More expensive than oak and maple, usually with rich depth of color even when unstained are the cherry, walnut and South American and African species.
Not technically a wood at all, but a fast growing grass. Green and sustainable. Comes in two shades, natural light or a medium dark shade which is produced not by staining, but by "cooking" the bamboo longer. Available in vertical, which appears as strips about 1/4" wide or horizontal which shows the actual profile of bamboo stalks.