Personally paid for Niagara launcher as I find that to be the far superior launcher to any other I've tried. My second one is Symfonium, the most feature rich and well developed audio player.
I have this one. It's the best Android calculator I've used.
I love the widget feature. You can add a whole calculator to your home screen, I have it taking up my second page, so whenever I need a calculator I swipe across once and it's there.