Really? Who needs a border-radius generator? It’s SO SIMPLE!
Actually, it’s a little more complex than that – I saw a great talk a while ago (I really should have blogged it) where the presenter explained a little known feature of border-radius. She explained, with some style as I recall, how you can have different horizontal and vertical radii on a single corner.
Oh yeah – funky shapes ahoy!
Really, would you expect this to be a single HTML DOM element with standard CSS?
However, it’s not as intuitive as a standard one value radius, so this generator from MDN helps to play around with the values until you get the shape you want.
[UPDATE 2018-10-17] Here’s a more modern version, with a nice interface, though the Mozilla version does have the ability to drag two points at once.