At James Randi's The Amazing Meeting this year, my friend and fellow astronomer Pamela Gay made a speech that covers a lot of ground, but essentially boils down to two ideas: do great things, and don't let the bastards grind you down.
The JREF put the video of her talk on YouTube, and it's simply fantastic.
She also paraphrased it for a post on her blog that's well worth your time to read: Make the World Better.
There's lots I could add, but there's no real reason to. Just watch this, and be happy there are people like Pamela out there in the world.
Now go out and make the world better.