Spanish Eclectic style blends design elements from Spain and Italy. You can tell this type of house by its low-pitched red roof, stucco siding, and arches.
Tudor style houses are reminiscent of the Tudor Period in England. They often have visible timber framing, parapets (a low, protective wall along the edge of a roof, bridge, or balcony), and gables. They most often also use brick as part of the exterior.
Colonial Revival homes have symmetrical brick or wood exteriors and gabled roofs. Most homes in this style use pillars or columns to frame the porch or entry. This style "was all about patriotism and a desire to retreat from earlier Victorian excesses and build something more authentically American." (MSN)
Contemporary homes are a sort of hybrid. They take design elements from an array of different periods and blend them together to make an ideal home. These homes also incorporate today's lifestyles into their floor plans. For example, many of them have a great room in which families can easily entertain and use in a multitude of ways.
I hope you've enjoyed defining the most popular American house styles! If you have any questions or comments, I would love to read them!