I’ll cast more votes for border-radius by corner, transparency in gradients (though I’d like to be able to specify the color in hex with a separate transparency value, not just RGBA), and multiple backgrounds. All fabulous ideas!
To the people saying gradients are already just as easily accomplished with images, think of the ways we have to expand the coverage of the image. Right now, there’s only repeating. You can’t stretch it in any way. I support the addition of background-stretch (despite the abuses that will come from it), but a CSS3-generated gradient would allow for much more interesting behavior possibilities that don’t require adding more images (read: bandwidth) to your site.