Via Dean Edwards' Links, meet
HedgerWow's <SELECT>-Free Layer, a CSS-only workaround for Internet Explorer's SELECT bug with z-index.
It's not quite clear from the demo, but I think the magic is an absolutely-positioned + transparent + huge IFRAME inside the layer to show. C'est trés hacky, but it still seems better (in a way) than the usual dynamic hide/show javascript approach.
Here's hoping that Microsoft will quickly windows-update us all with IE7 (which fixes this bug, hoorah), and free us of these sHACKles.