Have you ever read Howl's Moving Castle by Dianne Wynn Jones? You may recognize it from the Miyazaki film that was based on it. The book and the film start out similarly and then split off from each other so that the endings (and a lot of the middle) are completely different. I recommend both, of course, but this being the book thread, my point is that even if you've seen the film, the book is worth a read, and there are less spoilers than you think. It's also pretty funny.
One of the books I loved in middle school was The True Confessions of Charlotte Doyle by Avi. It's about a girl who is the only passenger on a ship when the crew decides to mutiny. It's suspenseful with a strong main character. It's been so long I can't remember anything about the writing style, though it was a Newberry Honor book.
Slower-paced, but Jacob Have I Loved by Katherine Paterson is also great. It's about a sister who feels like she is living in the shadow of her other sister, which is where the title comes from, a Bible verse about Jacob and Esau. The main character is a girl who crabs with her father and thus is more of a tomboy, and her sister is a gifted singer. It takes place in the 1940s on a small island so it's a nice historical novel. It won the Newberry Award.
And if you like nonfiction, try A Girl From Yamhill sometime. It's Beverly Cleary's autobiography. Again, not very suspenseful, but I found it pretty interesting. She's got another called My Own Two Feet which I'd like to read sometime, but haven't yet.
ETA:
Thought of a couple more.
Dairy Queen by Catherine Murdock. It's about a girl who decides to try out for her high school's football team. There's also some romance involved, but it's a part of the story, not the focus of it. It's part of a trilogy, but good as a stand-alone too.
Also, the Hunger Games Trilogy by Suzanne Collins. Only the first two are out, but the third is coming out this month. It's set in a dystopia where people are forced to face off in a Battle Royale-type game every year. These are fairly suspenseful.