I spent a few minutes knocking up a comparison table for a project today and wanted an easy way to have ticks and crosses. After a bit of experimenting I found out that the excellent FontAwesome project makes this quite easy:

<span class="fa-stack">
    <i class="fa fa-circle fa-stack-2x"></i>
    <i class="fa fa-times fa-stack-1x fa-inverse"></i>
</span>
<span class="fa-stack">
    <i class="fa fa-circle fa-stack-2x"></i>
    <i class="fa fa-check fa-stack-1x fa-inverse"></i>
</span>