So I made a topic on this over in The Lounge, and asked people about their six Desert Island Books, the ones they couldn't live without. I wanted to keep my reply here too, for posterity, and because my top books have changed over recent years as I have re-found books from my past I am reading to my son.
Here they are, in the order I first discovered them.

The Tale of Peter Rabbit - Beatrix Potter
Who couldn't love Peter and his gorgeous blue coat? I don't quite know the whole off my heart, but I adore it. Goblin loves it when I read to him, and this is a firm favourite in our house. I cannot remember the first time I ever read it, but the words are ingrained in my memory.

The Enchanted Horse - Magdalen Nabb
So I was a child who loved horses, and though I never understood as a child the references to God's Creatures in this slim novel, the descriptions captivated me. I had a version on tape (yes young ones, I used to have actual books on tape) and the voice of the narrator stayed with me my whole life. I can still recite entire passages by heart.

Pyramids - Sir Terry Pratchett
It's hard to chose one of the Discworld novels above all others, but though I adore Death, and Moist von Lipwig, and Angua, this is the only book in the whole series of 44 which is entirely stand-alone, and requires no other knowledge to work. I also love Pteppic, our reluctant King and hero, and I always empathised with him, because I've often felt like I was living a life which wasn't mine.

Venus As A Boy - Luke Sutherland
This was I think, the first novel I owned with a gay/bisexual main character, and I was quickly enchanted by the descriptions of Orkney, and by the strange journey the main character undertakes as he grows up. I read it over and over again, and it was the only book I took with me around the world. I read the whole thing in stages to my second boyfriend, just before we got together, and it set the tone of our relationship in a strange way.

The God Eaters - Jesse Hajicek
No couple in any other book have made my heart pound the way Kieran and Ashleigh do. Their world is rich and deep, their challenges enormous, the descriptions richly detailed, the conversations pithy and realistic. The blend of magic and logic is perfect, and throughout it all, their relationship makes me want to cry and laugh and shout with joy.

Now Is The Hour - John Spanbauer
for a long time after starting this book, I didn't understand it, or understand why I loved it so much. But John Spanbauer is the only person I've know of who has ever managed to describe the awe and majesty of Thunderbird, the hopelessness of death and betrayal, and the harshness of falling in love when it doesn't go well.

What are your Desert Island Books?