Not to knock Twitter Bootstrap off the pedestal, but Zurb Foundation is also pretty good. http://foundation.zurb.com/
It looks a lot like Bootstrap because it's based off it I believe but it's also responsive and has stuff to handle different device types which is pretty cool.
BTW, I don't have any connections to Zurb whatsoever
When I looked at Zurb vs Bootstrap, I wanted to use Zurb but the default form styling turned me off. When I am looking for a style guide the first thing I do is find the forms cause that is IMO the most difficult part of styling a web app.
To each their own. It's largely a matter of opinion and getting forms right is tricky, but from an accessibility standpoint, I much prefer Zurb's forms... much better contrast and easier to read.
I agree that for forms - bootstrap has it much nicer. It wouldn't be hard to transplant one into the other depending on your needs (responsive vs forms)
It looks a lot like Bootstrap because it's based off it I believe but it's also responsive and has stuff to handle different device types which is pretty cool.
BTW, I don't have any connections to Zurb whatsoever