With our boys, I think they're more interested in what they can do in their rooms, than how the room looks! As the old saying goes, "Busy boys are good boys!" ;)
One of the first areas we painted when we moved in, was a wall in our oldest son's room... turning it into a giant chalkboard. Then, last year, for his 11th birthday we gave him a fairly heavy-duty indoor hoop (since our boys had gone through many over-the-door, smaller hoops). He "shoots hoops" nearly every day in his room. While he also likes to play basketball outside, this one is nice when the weather is bad. It's also fun for him since it's not as high as an outdoor or gym hoop so he, his cousins and friends can dunk on it! :)
A marquee initial above our middle son's bed provides a fun focal point. He has a lego table in his room where he enjoys building. The "bazillion" legos are kept in large tubs underneath his lego table (for the most part ;).
Our youngest, who is crazy about sports, uses his train table as a football and baseball field. By cutting a piece of artificial turf, taping the edges with green tape and then using white craft paint for field lines, a train table is easily converted to a child's field of dreams! ;)
He collects mini helmets and also plays with these mini sports figures.