This link (here) may not be exhaustive (but it might be), but it offers a useful list of attributes that can be applied to custom controls to support better design-time interaction.

I find it useful to be able to right-click a property in the designer and select “Reset” to return it to the control’s default value. Much more important is the ability to automatically tag a property as localizable so without any other code it’s value will be initialized from the resource file.