For those that are looking to save time with rapid development you can check out Zurb's Foundation framework. http://foundation.zurb.com/
Here is a free WordPress theme based on their awesome framework which is responsive and very customizable.
I used foundation for years, and it really is a great framework. However, since I discovered Semantic UI, I simply can't find a good enough reason to switch back. I just find it much easier to develop and create prototypes on Semantic. Check it out.
I happen to be the one in charge of the official WordPress theme for Semantic, if you want, you can check it out here.