Nanocomposites are very promising for new lightweight materials with significantly improved mechanical and electrical properties. We advocate graphene-based nanoparticles as the filler component for such composites. Based on a newly developed method, we are able to produce functionalized graphene sheets in bulk quantities. For the performance of the composites the properties of both of the filler particles and the interface between the filler and the matrix are important. Using scanning probe methods we investigate the structure of the functionalized graphene sheets, and we are able confirm our results with models based on first principles. For future experiments we propose using atomic force microscopy and single-molecule atomic force spectroscopy to study the interface between the sheets and different potential host materials to predict the behavior of the composites and optimize their performance.