Nocturne - no fair! Don't raise hopes like that!
I find one of the compelling arguments to wanting a built-in GUI editor to be the cross-platform nature of GameMaker. I would like to have a system that works exactly the same regardless of whether the user is using keyboard, mouse, touch screen, Windows, Mac, Android, iOS and so on and so forth. That seems to limit functionality by using GML alone.
I've actually started putting together "my own" local package based on a "Buttons 2.3" tutorial by SamSpade, because my first game's GUI was nasty (seriously, I should have broken the GUI out into a separate project in the first place). A problem with the marketplace is that one needs to search the MarketPlace, finding numerous packages with old code, external libraries (e.g. .dll) that preclude Android, and so on. Long, long ago I toyed with Visual Basic where one drew basic controls onto a form - it has long boggled my mind that GameMaker doesn't have a similar system.