If you want to open the (existing) pages in a popup window when a selection is made you can use code like this:

    <apex:page>
        <apex:form>
            <apex:selectList size="1" onchange="return selectChange(this);">
                <apex:selectOption itemLabel="--None--" itemValue=""/>
                <apex:selectOption itemLabel="ABC" itemValue="/apex/A?id=123"/>
                <apex:selectOption itemLabel="XYZ" itemValue="/apex/A?id=456"/>
            </apex:selectList>
        </apex:form>
    <script>
    function selectChange(select) {
        window.open(select.value, '_blank');
        return false;
    }
    </script>
    </apex:page>

where instead of the above hard coded `apex:selectOption`s you would create then in your `apex:repeat` loop.