1. First moment: "Dalek"
2. Last moment: "The Stolen Earth/Journey's End"
3. Ultimate moment: "The Parting of the Ways"
4. First moment: "Aliens of London/World War Three"
When he went all Hackers on the Torchwood and Royal Navy databases to help the Doctor defeat the Slitheen. He even put his brave face on to save Rose's mother, Jackie, even though she spent the better part of a year blaming him for Rose's disappearance.
5. Last moment: "Journey's End"
6. Ultimate moment: "Army of Ghosts/Doomsday"
7. First moment: "Boom Town"
8. Last moment: "Gridlock"
9. Ultimate moment: "Bad Wolf"
10. First moment: "Smith and Jones"
11. Last moment: "The Stolen Earth/Journey's End"
12. Ultimate moment: "The Doctor's Daughter"
13. First moment: "Partners in Crime"
Using her seemingly nominal skills as an office worker, she starts investigating weird phenomenons and ends up taking down a worldwide weight-loss corporation run by aliens (I know, just stay with me) and finds the Doctor again in the process.
14. Last moment: "The End of Time"
15. Ultimate moment: "The Poison Sky"
When she's alone on the Sontaran battleship and takes a few of the talking potatoes out, then restarts the teleport pods to get the Doctor back to her. Not bad for a temp from Chiswick.
16. First moment: "The Beast Below"
She helps lost and crying children, saves the last of a rare and magnificent space creature, and gives hope back to all of the intergalactic version of Great Britain. All while in her nightgown.
17. Last moment: "The Angels Take Manhattan"
With Rory. On a building ledge. 1938 New York City. I can't see though the tears.
18. Ultimate moment: "The Girl Who Waited"
19. First moment: "The Vampires of Venice"
Upon entering the Tardis for the first time, he knows it's another dimension and isn't surprised like every other being that has ever stepped inside. The man is prepped and ready!
20. Last moment: "The Power of Three"
It's the last time we see Rory the nurse (not the most impressive of his monikers, I know) saving lives left and right during the slow invasion.
21. Ultimate moment: "Let's Kill Hitler"
That time he punched Hitler in the face. I mean, duh!
22. First moment: "The Time of Angels/Flesh and Stone"
23. Last moment: "The Name of the Doctor"
24. Ultimate moment: "The Wedding of River Song"
When she was willing to let the entire universe burn so the Doctor could see that he would be missed if he died. But that she would miss him most of all. Hell, I would marry her after that!
25. First moment: "Asylum of the Daleks"
26. Last moment: "Dark Water"
27. Ultimate moment: "The Snowmen"
Unfortunately not every companion gets to travel through the stars in the Tardis. But that doesn't make them any less kick-ass.
Case in point:
28. Ultimate moment: "Voyage of the Damned"
29. Ultimate moment: "Closing Time"
When he decided to just pretend like he knew what was going on to take down the Cybermen. NO FEAR!