Since wireframing for websites and apps is pretty much at the core of my day-to-day work, I'm forever creating (and re-creating) simplified UI elements. Over time these have built up into a library that I can call upon whenever needed and since I find it so useful, I figured others might as well.
Created in Illustrator CS6, the file includes all elements as editable vectors and as a pretty extensive Illustrator Symbol library for easy use across multiple documents. Check out the preview below and if it could be useful to you, grab the free download here
I hope this kit comes in handy and let me know if you can think of anything obvious that I've not included.