After finishing the "Wanted: Dead!" mission in the Secret Armory DLC, you need to go to a Crimson Lance outpost to collect your reward. The location is a bunch of wanted posters of the Vault Hunters. Upon turning in, your character leaves this behind.
Tannis on the final mission when you're off to kill Steel.
Patricia Tannis: Hey, for me, take that bitch down.
Crawmerax solo. You're going up against one of the biggest, baddest things to be found on Pandora at the moment, easily able to slam you to within an inch of your life when you're at your strongest, easily able to demolish entire towns with no effort; as well as his lackeys, which, while not the size of the White House, are still stronger than basically anything else in the game save Crawmerax himself. Then you, with either your turret as a shrewd distraction, your pet as a debilitator, your ability to step in and out of the human dimensions for a short period of time and completely heal any wounds you might have taken, or just through violent application of your BARE GODDAMN HANDS, take this beast down completely on your own and collect enough wealth to make the legend of the Vault seem like peanuts. It's pretty amazing.
The entire ending to The Secret Armory of General Knoxx. You reach the armory, looting as many weapons as you can. Then the countdown ends, and BOOM! You watch the entire place explode in what is arguably the most awesome cutscene in the entire goddamn series. The best part? You survive the explosion, and you don't even know how.