<HR> tags can be pretty cool. There are all sorts of things that can be done with them. I've got some examples below. Below each visual example is the HTML code needed to display it, with the text color being red.

This is your standard <HR> (Horizontal Rule):

Here is a nifty little trick, but it only really works on non-black sites.

Here is the same thing, only thinner.

Same sort of thing, except without the noshade, and a different size.

Same thing, with a bigger size.

You can also mess with the width. The width on this will always stay the same distance away from the border, even if you resize the window.

You can have any width= percentages. Here are some more examples.