Really cool new app from the folks over at MacRabbit. You name your layers and layer groups with file extensions, drag the .psd into Layer Cake, and BAM. It saves your layers and groups out as their own files.
And per usual with MacRabbit, Layer Cake is visually stunning. The attention to detail is impeccable, and little touches (such as the saving animation) give it a really strong personality. MacRabbit is easily one of my favorite Mac app dev shops.