I want a widget like the properties window in Visual Studio or NetBeans. It basically has two columns: the name of the property on the left, and the value on the right. The value needs to be able to be restricted to certain types, like 'bool' or 'float' (with valid ranges), but should also support more complex types (perhaps requiring a popup dialog when clicked, and then it can just display a toString() version in the window. I'm sure I can add most of those features myself, but what's the best base widget to start with?
Oh... grouping of properties is good too (like a tree I guess). And property editing should invoke a callback (send a signal).