Scenario:
"I want to create a valid XHTML drop down menu (with submit onchange) for things like <%archivelist%> and <%categorylist%>."
Solution:
Use the onchange attribute in your list, which is defined in your template.
Original forum thread (thanks, moraes!):
http://forum.nucleuscms.org/viewtopic.php?p=19698#19698
Method:
Use the following code in your template.
Archive List Header
<form> <select name="archives" onchange="window.location.href=this.form.archives.options[this.form.archives.selectedIndex].value"> <option value="">Archives</option>
Archive List Item
<option value="<%archivelink%>">%B, %Y</option>
Archive List Footer
<option value="./archives/<%blogid%>">All</option> </select></form>