8. Amy Pond, "The Beast Below"
In her first proper outing as a companion, Amy discovers the future of the UK following an Earth near fiery extinction and soon uncovers a dark plot there - the Star Whale the UK contingent is travelling on is being tortured to keep it flying, causing immense suffering. The Doctor is horrified and disgusted, planning to euthanise the Star Whale and ends its suffering but Amy looks over everything she's seen and heard and disables the controls, allowing the Star Whale to be free and actually fly quicker. It's this compassionate view that she's taken from watching the Doctor and her own incredible problem-solving skills - later seen during her takedown of a video-camera Weeping Angel in the same season - that make this such a great, joyous moment and a heroic beat that secured Amy in our hearts as a true companion.