Paralysis is one of my favourite statuses to abuse, as the loss of speed and chance of a useless turn is too good to pass up. It's also easy to inflict, with Thunder Wave being commonplace among defensive Pokemon. Burn is nice, too: it's great seeing your opponent's attacks suddenly do pittance as their health is slowly wittled away.
While Freeze differs from the above two in that it's difficult to inflict, it's really entertaining to see your frustrated opponent let out a tirade of curses as they roll the dice to thaw out their Pokemon. They can be frozen indefinitely, and they become completely useless when frozen. Difficult to land, but great to watch.