I made these a while back for Glest Advanced Engine.  The background is from the Glest team, used with permission.  Attribution goes to them (along with a link to Glest.org).  Credit to me would be nice, but I won't require it.  Included are buttons for shrink (minus), grow (plus), close (x), as well as up and down arrows.  Each has a white and orange variant.  All icons are very small (32x32px) because they're intended for in-game GUI elements like the mini-map.

The xcf file includes all the icons and the background as layers.  The zip includes them all as separate png images.