Is there a list of WordPress CSS id/classes that I can use to build plugin option screens that look and feel more like a normal WordPress option page? I have found some through serendipity but it would have been nice to have a list.
An example is this class: button-primary That makes a button look like this: 
We’re working on updating http://dotorgstyleguide.wordpress.com/ to have more of this information and reflect the style updates from 3.2.
Other than that, I’ve seen a plugin (that I currently cannot locate) that shows a demo page of sorts that displays the various CSS selectors and what they look like, but I believe it was outdated. Other than that, your best option for now may be to just fire up Firebug/Web Inspector and take a look at wp-admin/css/wp-admin.dev.css.