iOS Design Kit - The newest library of native iOS templates
Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Sketch Repo - Collection of resources for anyone who uses Sketch
Platforma - Wireframe library of layouts and UI elements
SketchApp.rocks - Index of all awesome things related to Sketch.
iOS Wireframing UX Kit - An easy, speedy way to wireframe for iOS