While I consider myself a jack of trade, UI Design is probably my most favorite. UI Designs can range from really modern and tech based (such as the GlassLink tablet, Twitter feed, and Datamyne UI) to elegant, soft, and artistic (such as the Sea Glass and Arctica UI).
Regarding the “artsy” UI’s, designs that are centered around nature and “natural” palettes are especially my favorite.. The Tumblr page Natural Palettes is filled with beautiful photos of nature along with their color palettes strategically placed on the photo. This is sort of how I came about the design for the Tundra UI in particular. The colors of cyan, grey, white, and black really bring about that natural “tundra” aesthetic.