Flat UI Pro is made on the basis of Twitter Bootstrap in a stunning flat-style, and the kit also includes a PSD version for designers. From $39. Learn More: http://designmodo.com/flat/
Clean, minimalist, nautical inspired UI kit, spread across 4 content categories. Containing 100+ elements and a style guide that will help you build your project in a snap! Compatible with Photoshop & Sketch!