Best for me: Bialetti moka stovetop espresso maker- I use this for my morning coffee everyday. Our Vitamix blender is pretty awesome/useful, too. Also if cast-iron pans count as gadgets, then I love my cast-iron pan as well. Perfect for frittata, cornbread, etc...!
Worst: so far ive only used my crockpot once but I think that just reflects badly on me, not the crockpot!