Nicer alternative to the default Rails scaffolding stylesheet: scaffold.css?
I'm going to assume the others are answering the wrong question with their focus on scaffold generation and guess that you really just want more attractive css.
I'd suggest blueprint css framework which has fairly attractive defaults. It's not specificly designed to replace scaffold.css but it doesn't take much to make it work.
You honestly don't need one. Why? Because you're not supposed to be using that. A scaffold is precisely what it is, something there to help you while you're building your app, but not a system for the long term.
However, if you just want something that doesn't look like the graduate class at Playskool My First Web App produced, try Ryan Bate's (Railscasts Guy) Nifty Generator gem at http://github.com/ryanb/nifty-generators/tree/master. Not only does it look slightly better, but it has some nifty extras built into it.