As for Php there are loads of Theme frameworks warp5 etc. But is there a single Theme framework OR some framework with which I can rapidly develop wireframes and prototypes for new website being created. I primarily use 960Gs for the css stuff. but this isn't a consideration for the theme framework you suggest. I am open to suggestions on the Css parts too.
If you were using JQueryUI that is pretty easily themeable http://jqueryui.com/themeroller