The two favourite designers I personally like is Tokidoki and Paul Frank
Tokidoki and New Era got together recently to produce a series of caps that feature the distinct character style that made Tokidoki famous in the first place. Each cap is individualized with pop aesthetics and great use of solid colors and dark tones, and some feature characters from Marvel and Sanrio to add a triple collaboration aspect to the release. Furthermore, under the visor is a comic-like design that tells a short story or what looks like one scene from a larger story. I think they are fantastic and some great designs. You can buy them here.