Ooh I like this thread.
Let's see...
I can definitely kind of relate to Hermione Granger (from HP obviously). Loves learning and is reading constantly, isn't very girly, and can be a bit shy. Not to mention we both have frizzy hair.
She's more talkative than I am though and a lot smarter, plus she's a total badass. ;]
Sam Winchester from Supernatural is another one. He's always figuring things out, great at searching and hunting down answers, also constantly reading and is very studious, mostly quiet and keeps to himself (although he isn't exactly shy), he's sensitive of others and will speak his mind when he has to. I don't exactly wear my heart on my sleeve, rather I tend to bottle things up, but he has those moments too. He also has this dark side of himself he doesn't like to show nor dwell on. I know there's a lot more to it, even if it's rather fictional because of the storyline, but part of that "darkside" is intense anger, sadness, loneliness, and just a jumbled up mess. I can definitely relate to most of how he feels sometimes.
Kerry Hennessy from 8 Simple Rules is probably my fictional character high school/teenage alter ego. Even out of all the books I've read and tv shows/movies I've watched, she's probably the most relatable to me. She's short, like me. She can be incredibly sarcastic and has dry humor, like me. She's extremely introverted, gets annoyed with other people easily (especially her siblings), is another character who always reads (I like people who read, okay?), and she's smart, like me. Oh and I love animals just about as much as she does. The things she gets upset over are pretty much the exact things I got upset over in high school too (and I still feel like this sometimes) -- no one liking me, was never pretty, getting teased, being used by kids just for being smart, being jealous of my sibling because they were better liked and were better looking, being too shy and quiet, etc.
Edit: Added pretty pictures.