How to align 3 divs (left/center/right) inside another div?

I want to have 3 divs aligned inside a container div, something like this:

[[LEFT]       [CENTER]        [RIGHT]]

Container div is 100% wide (no set width), and center div should remain in center after resizing the container.

So I set:

#container{width:100%;}
#left{float:left;width:100px;}
#right{float:right;width:100px;}
#center{margin:0 auto;width:100px;}

But it becomes:

[[LEFT]       [CENTER]              ]
                              [RIGHT]

Any tips?