Full code after the jump.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/08/08/positioning-a-label-within-a-progress-bar-using-the-progressbarlabelplacement-property/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Label text="ProgressBar.labelPlacement" />
    <mx:HBox>
        <mx:VBox>
            <mx:RadioButtonGroup id="rbg" />
            <mx:RadioButton label="left" group="{rbg}" />
            <mx:RadioButton label="center" group="{rbg}" />
            <mx:RadioButton label="right" group="{rbg}" />
            <mx:RadioButton label="top" group="{rbg}" />
            <mx:RadioButton label="bottom" group="{rbg}" />
        </mx:VBox>
        <mx:VBox backgroundColor="white"
                horizontalAlign="center"
                verticalAlign="middle"
                width="200" height="100%">

            <mx:ProgressBar id="progressBar"
                    barColor="haloOrange"
                    label="{rbg.selectedValue}"
                    labelPlacement="{rbg.selectedValue}"
                    mode="manual"
                    width="150"
                    creationComplete="progressBar.setProgress(50, 100)" />

        </mx:VBox>
    </mx:HBox>

</mx:Application>

View source is enabled in the following example.