I have several that really stick out in my mind:
Season 5 - when uber-competitive Mark waited for Ali Vincent near the end of the race so they could cross the finish line together--she carried him on her back.
Season 7 - when, after everybody had put extra weight for Tara to carry, she pulled the car ahead of everyone, especially the Tongans.
And...on the Australian version season one, I mini-crushed on Shane Giles so I liked when he did his fear challenge down the cliff and also the finale, where he looked so hot that Jillian proposed to him.