How to center a ul (nav) that has flexible width

I am trying to create the nav of

http://forrst-production.s3.amazonaws.com/posts/snaps/59125/mega.jpg?1297328693

the nav width will expand or contract 开发者_JAVA百科according to the width of inner list items. How can I acheive that? or must I set a fixed width for the nav?

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Make each item and the ribbon ends display:inline-block, then use text-align:center on the parent.