Not sure what your idea of flat means with a launcher since thats more up to the theme you choose, but if your looking to get away from the stock launcher look I really like Kvaesitso, ive got it setup to have 3px of rounding and 80% transparency with blur

If your looking for a more skeuo look turn the opacity of your background boxes way down and it can look prettt good with a more skueo icon pack

Wallpaper by me!