Every once in a while even I have to do a little design work. Here are some helpful PSDs I’ve used to get it done.
960 Grid System – the classic desktop-first grid system
Bootstrap 3 PSD – mobile-first, responsive grid for Bootstrap 3
iPad GUI PSD – all the iOS 7 GUI elements in editable, vector-based format
iPhone GUI PSD – just like the iPad PSD, but for the iPhone
OS X Cursors – common cursors for Mac