What are some important quotes from The Lightning Thief?

I think that the opening chapter has some great quotes that are important to the story and Percy himself.

Look, I didn't want to be a half-blood.

The previous quote is the first line of the book. It's important because it shows readers that Percy didn't choose to be a half-blood in the way that Bella Swan chose to become a vampire. Instead, Percy's lineage has been thrust on him, and he has no choice in the matter. He can absolutely try to ignore his lineage, but that ultimately doesn't change anything. He is what he is, and he has to accept it.
Another good quote follows shortly after the previous quote.

Being a half-blood is dangerous. It's scary. Most of the time, it gets you killed in painful, nasty ways.

This is an important tie-in with the previous quote because it shows readers a couple of things. We have no idea what a half-blood is or what it means, but this quote all of a sudden shows readers that it is likely a bad thing. Additionally, the wording of the quote hints at the idea that the narrator is speaking from personal experience. It's telling us that he has been in those situations and has lived to tell about it.
In addition to being a half-blood, Percy has really low self-esteem about himself, and readers are clued into this fact with the following quote.

I wondered how she could say that. What was so great about me? A dyslexic, hyperactive boy with a D+ report card, kicked out of school for the sixth time in six years.