The best book find I’ve ever had happened at Half Price Books, several years ago.
I was looking through the stacks, looking for some sci-fi, as was my girlfriend. She got rather excited, as she’d just found a copy of So Long and Thanks for all the Fish, by Douglas Adams. Hardbound. She’d never read it, so she decided that was what she wanted, but wanted to make sure I didn’t have it. I assured her that I didn’t… and so she opened it up to the first page to see how much they wanted for it.
“Oh my god, Lightnin’? Take a look at this…”
On the first page it said, “To Lightnin’, Best Wishes, Douglas Adams”. Holy crap- not only signed, but to ME.
That was my Christmas present that year. 
A few years later, Douglas Adams came to town to push the game he worked on, Starship Titanic. We went, of course, and took the book with us. When we got up to him, we put that book in front of him. He opened it up, and when he saw that he’d already signed it, he started to ask us what the deal was.
We explained how we’d found the book, and pretty much just wanted him to know how special it was to us.
He signed it below, “And Again, Douglas Adams”.
So, yeah, I’ve got a book not only personalized to me, but signed TWICE by the author.
Needless to say, we mourned his passing. Great guy.