I’ve used Nifty corners before they were always pretty good. But I’d imagine a fair chunk of them rely on javascript too.
More recently I decided to approach this in a progressive way rather than bending over backwards for the older browsers. There’s now a CSS3 property which will create rounded corners for you and you don’t need to depend on javascript, background images or anything else.
IE versions before 9 won’t support it but that’s what I was saying about progressive enhancement: give a better experience for the more standards compliant browsers and in turn future proof your site whilst still giving the older browsers a decent experience that still works (just without rounded corners). Same also applies to drop shadows. That can also be done is CSS3 too.