You are a little off there, Aaron. Modern architecture (with a capital M) was not created by the Bauhaus, though Gropius, Meis Van der Rohe and others were very influential. Modern architecture came about as the result of explorations by a number of architects around the turn of the twentieth century. These explorations paralleled the social, political, scientific and artistic changes occurring at the time. The architects were looking for new forms to recognize these changes.

Postmodern architecture, as the name implies, was a reaction to the international style modern architecture that came about as a result of those earlier explorations. It offered a return to many of the iconic forms, (sloped roofs, classical columns etc.) colors and references that were not a part of the modern agenda. Thus, it is not really modern, nor is it strictly traditional either. Of the architects best known for producing postmodern work, some like Robert Stern have gone more traditional, others like Gehry used it as a bridge to move past modern and still others have created a personal style that is really theirs alone.

Contemporary architecture is primarily real estate term coined to refer to anything non traditional. It is often used indiscriminately as splatgirl emphasized. I think that, most accurately, it identifies a strain of architecture, influenced by F. L. Wright and Charles Moore that combined sloped roofs, open plans and an affinity for natural materrials. Sort of an attempt at a best of both worlds approach. It actually developed concurrantly with Postmodern and for many of the same reasons.

Post modern design, and to a lesser extent contemporary design, has influenced much of the architecture we see today. Those working in a more mainstream modern architectural style are indebted to many of the material and color explorations of postmodern. Similarly, a lot of the environmentally conscious design today has its roots in the contemporary architecture of the seventies.

I think the term modern (with a small m) is more akin to the term traditional in that it encompasses a number of styles. Mid-Century Modern, Art Deco and International Style Modern are as different from one another as Classical, Gothic and Victorian.