Fieldset
It helped me reducing quite some numbers of <asp:panel> I was using just to have a nice border around other controls or to give a better structure to my page.
If you workon an Intranet project with IE, you can use a <Fieldset> tag that do perfectly the job without any server roundtrip.
Plus the possibility to include a <Legend> tag inside to write the Title of the box over the border 'a la' Windows ;-)