Here's another cool freebie if you're looking for some no-hassle rounded corners.  It's called Spanky Corners, and it's available from SitePoint.  Just punch your colors in, select your radius, and it gives you some small .gif's complete with the html and css to put it all together.  I haven't tried it out extensively, but it's a pretty cool idea.  The only caveat I see at this point is that it doesn't support any borders.