WinForms PropertyGrid
I'm probably the last person on earth that didn't know that you could use the PropertyGrid in WinForms apps. Well, I found out today, and I'm liking it so far. It doesn't show up by default in the Toolbox, but you can add it with the "Add Items" dialog.
So did you know that you can bind the PropertyGrid to an object? Further, it works exactly the same way that VS design-time support works. This means that you can decorate your objects with attributes from the System.ComponentModel namespace, and they will affect how the properties are displayed inside the grid. Don't want a property to show up? Well <ComponentModel.Browsable(False)> is for you. Want it to display neat little tips in the help space at the bottom? Use the Description attribute.
I can't wait to play with this some more.