"Run" Forrest "Run" Vanderbilt in Season 2, who set a record of 01:06.9 for the Qualifier and only wiped out once (on the Big Balls). He goes on to win the episode.
"Freak of Nature" Frank Beasley in Season 3 was one of the three people to ever successfully cross the spray-paint-spewing season 3 Sucker Punch, which downed pretty much everyone else. He also completes the rest of the Qualifier with only one wipeout on the Big Balls (much like Forrest's run, and Forrest didn't have a Sucker Punch wall to cross). He goes on to win the episode as well, completing in half the time as the second-place contestant.
Rico "Thunder" Curtis got through the Shapeshifterwithout having to ride around on the shapes, by jumping through in an amazing leap. Sadly, unlike the other examples, he gets knocked out in the second round.
The "Board Gamers" in Season 3's Family episode used the strategic skills honed from playing board games together to dominate the Wipeout Zone. The son, Tom Cardiff, posted the fastest time of all contestants on that particular course (4:45), and the mother, Jamie Cardiff, finished in 9:12, the fastest time of any female contestant and 5th fastest time overall (and at 48 years old, no less).
Jacob "Dancin' Fool" Chrisman had the fastest run in the Qualifier - 4:06.6 - of his Winter Wipeout episode. He took first place in Rounds 2 and 3. In the Wipeout Zone, he won with a time of 3:46.15, twenty seconds faster than his 1st place Qualifier run, and managing to win all four rounds.
"Where's the pole?!" aside, Ariel Tweto deserves a mention for her successful Seal Hop across the Big Balls, becoming the first contestant to successfully cross them.
In the 2012 season episode of Bosses and Employee's, an assistant gym coach not only dominates most of the 3 rounds (as opposed to his boss), but in the Wipeout Zone, he manages to speed through the first obstacle without even pausing on the small rest area after the first rotating windmill.
In Series 2, episode 2 of the UK version, Rachel survives the sweeper by grabbing onto it and outlasting the other person who had grabbed onto it. Then she climbs off on another platform, too.
Andrew "The Cowboy" Sherman in Season 3, after coming in first on the Qualifier, easily overcame the Double Cross by quickly charging across it in seconds without wiping out. In the Wipeout Zone, he won with a time of 3:46.21 and only two wipeouts.
In the beauty queen episode, the second round has awesome all around. "Banana Queen" Amanda Delgado clears the whole thing on the first try, "Ms. Hot Stuff" Wendy Napp actually stands on the sweeper bar and jumps from there to the platform (declared by the Johns to be a show first), and at least three of them climb up the tilting platform at full downtilt before the finish.