Several mentions of Enid Blyton early in the thread with comments that her books are out of print. Many are still in print in the UK; I couldn't let my children miss out on "The _____ of Adventure" series, so those we couldn't find from the library, I had a friend's "mum" buy in England and ship here. You can also purchase via Amazon UK (but you will probably have a foreign transaction fee, and call your credit card company before you order, or they may reject the transaction). Hefty shipping, but for a great book... And I think I picked up one or two used on the internet in the US.
Others my Ds really liked that haven't been mentioned yet:
Snow Treasure, by Marie McSwigan - About kids helping smuggle gold out of Norway on their sleds during WWII. The book blurb claims it is based on a true story, but I have been reading up on WWII in Norway and haven't found any references yet. But it is still a thrilling story. I think gifted D read it in 2nd grade, maybe.
Bill Bergson and the White Rose Rescue, by Astrid Lindgren (someone mentioned the other Bill Bergson book above, but this one is my favorite). A little scary, but very thrilling. One of those "kids on their own against dangerous grownup" stories. With a Scandinavian flair.
The Case of the Silver Egg, by Desmond Skirrow. About a club of boys in England who rescue a kidnapped scientist and his invention. The boys are obviously gifted, so our kids would find it an especially fun read
For picture books, our all time favorite was "I, Crocodile" by Fred Marcellino. It is a hilarious account of a crocodile brought back to Paris by Napoleon. Smart, sly, and funny.
For early teen girls: The Beekeeper's Apprentice, by Laurie King. It is about a 13 year old girl who becomes Sherlock Holmes' apprentice. Again, I think my D loved it so much because she is very like the gifted female girl in the story. There are several more in the series, but that is the one that D read until it fell apart.
And for those who mentioned the Moomintrolls -- D20 and I are going to Scandinavia this summer, and it is the 65th anniversary of the first publication of those books. We were trying to pick which ferry line to take from Helsinki to Stockhom, and the deal was clinched when we found out that Moomintroll characters are riding on the Silja line all summer. We didn't want to miss that!
