GTK+ style combo box
GTK-style combo boxes open up a menu-like list with buttons that slowly move up and down when you hover over them. I totally hate them, they're so clumsy to use, especially where there is a lot of items.
The Qt-style combo boxes with the scrollbar on the side are much nicer.
QtCurve has the option of making Qt have GTK-like combo boxes, but not the option of having GTK use Qt-style combo boxes.