Windows Clock Replacement
It allows you to display the date, seconds, and day of the week, I hated having to hover over or double-click the freakin' clock just to see what the current date is (yes, I'm that lazy).
The install was quick and painless and integrates well with the Taskbar; meaning it doesn't cover any of the tray area or blend strangely, depending on the skin you pick, it looks pretty much as if it were built into Explorer, except that it uses images instead of a font, so text spacing isn't exactly ideal.
Either way, this is a great add-on that Windows *should* have built-in.
Screenshot Sample (from their site):