SplitButton is a free, open source, button control that allows you to add menus to your buttons similar to Office 2003 and Office 2007 buttons. This type of control is frequently called by other names such as "menu button," "split button," and "drop down button." SplitButton is written in c# and works with all .NET languages (VB.NET, C#, etc.).
Features at a glance
SplitButton works with either ContextMenu or ContextMenuStrip controls. SplitButton also correctly renders with the visual style of the operating system.
How to use SplitButton control in your application
http://wyday.com/forum/viewtopic.php?f=2&t=24