Rick Womer , Jan 18, 2010; 09:59 a.m.
Of the cameras you list, all are "entry-level" with lots of automation and presets ("action", "portrait", "scenery" etc.) except the K20D. It is a no-nonsense, weather-sealed camera that is marketed for "enthusiasts", though I know several pros who use them. The price:performance ratio is outstanding with Pentax. The drawbacks are the lack of video (can you dig up another $300 for a K7?), and some find that the K20 AF is not as well suited to fast action as Canon and Nikon.
There is also an extremely helpful and friendly Pentax community here, and at pdml.net.