This is one a lot of people know, but it's worth covering again because it's easily forgotten as it's a small detail. Since we do eFinance sites, we often don't want folks' UserNames collected and stored in AutoComplete, especially when the site is browsed on a public machine.
<form id="formSignOn" autocomplete="off" method="post" runat="server">
Note that autocomplete="false" doesn't work. However, autocomplete="off" works in both IE and FireFox.
Thanks to Johnson Michael for reminding me of this tip.