I agree with you about the rosette corner pieces. Why spend $5 on a 5 inch square piece of wood that just screams "I am too lazy to mitre"

I don't know that it's called, but I like the door trim that reminds me of an mantle on the top. Like in the top left of the attached picture. I think they may be called Architraves. http://www.door-window-moulding.com/NWM2006Cat/NWMoulding06-04.htm

I have also seen what you are talking about called a crosshead. Here is a link www.crossheaddepot.com

Crosshead Depot has changed their name to www.overthetopdoortrim.com apparently. I really like their products, since they are all-wood constructed and not that cheap foam stuff for about the same price.