#jquery.mutuallyExclusive
This plugin can be applied to sets of identical dropdown menus on a page. When applied, it keeps track of which items have been chosen and removes those items from other dropdowns on the page.
For example, say you have a form with two identical menus, each containing a list of colors. If an option with the value "blue" is slected in the first menu, the option with value "blue" would it would be removed from the second one. If "blue" is subsequently unslected, it will be added back.
To use, select the group of select boxes, and call the method on it.
<select class="colors">
<option value="">--Select Your Favorite Color--</option>
<option value="red">Red</option>
<option value="white">White</option>
<option value="blue">Blue</option>
</select>
<select class="colors">
<option value="">--Select Your Favorite Color--</option>
<option value="red">Red</option>
<option value="white">White</option>
<option value="blue">Blue</option>
</select>
$("select.colors").mutuallyExclusive();
check out how it works on JSFiddle: http://jsfiddle.net/NH874/15/