150+ Free UI Kits For Designers (Updated) - Hongkiat
70 Greatest Free Photoshop PSD UI Kits / Wireframes for Internet & Smartphone Apps - EGrappler
GitHub - bootflat/Bootflat.UI.Kit.PSD: Bootflat UI Kit is PSD User Interface Pack including a set of beautiful and pure components, which you can use to create startup projects, websites or iOS/Android Apps.
Transparent UI PSD Kit - Free Photoshop Brushes at Brusheezy!