Rafal Tomal has shared with us his Free Photoshop Wireframe Kit. Though it is little old but this wireframe kit is worthy for quick development. It includes Notes, Images & video, Form fields, Headings, paragraphs and bullet lists, Navigations, Ad banners and Common website elements like: search box, email sign up form, etc.
In order to use it, you need to simply open a blank Photoshop document in one of my screens and the wireframe kit PSD in the other one. Then, drag the elements you need from one document and drop them into the other one. As you can see, all elements are black in my wireframe kit. You can easily change the background by managing the opacity of the element.
There is no special license on this wireframe kit. Feel free to modify it and share it with others. Simply, do whatever you want with it.