CSS Library: Horizontal CSS Menus: Here
Half moon tab menu
Author: Dynamic Drive
We named this CSS tab menu "Half Moon" based on its look. The menu uses a transparent background image for each tab item to create a right round edge. This transparency means you can modify the colors of the menu items (such as the hover color) just by changing CSS color values inside the style sheet. Easy alignment is also supported, so you can, for example, align the tabs center or right if desired. Nice!
The single image: