Enid Blyton is good for a precocious reader who likes mysteries.
If you want contemporary, I'd strongly recommend Wendelin Van Draanen's Sammy Keyes Mysteries. I think the first one is either Sammy Keyes and the Skeleton Man or Sammy Keyes and the something Hotel.
Sammy is a total hoot. She is a 7th grader who always finds herself in trouble and at the center of something that needs solving.
I remember enjoying 1 minute mysteries around then, if that's what it's called.
And The Westing Game! Good call.
But I really loved the Tommy and Tuppence ones best at that age. Not sure why.
Me too! I reread one recently and still loved it, actually. It's because Tuppence is the best -- she's all cute and independent and capable and fun.
Actually, I need kid present book recs, too. My cousin is 6, but a really good reader. He read the first two Harry Potter, but they got too dark for him. Lemony Snicket ditto. My aunt mentioned things like Superfudge, but now I figure everyone else will get him that. I was thinking Phantom Tollbooth, but I wonder if he'll get the jokes?
As long as they aren't scary, I guess.
Maybe some Roald Dahl, Jesse?
Tommy and Tuppence were cool...very happening for 1925 or whenever...and there was a show, on pbs with a Francesca somebody... my one junior high friend and I got a big kick out of them. Yeah, I was softer-side Willow, then.
My word, how did I forget Blyton? Thing is, there's the probable need to warn a modern kid about the racism (not to mention the sexism) of the period - I remember liking the books, but thinking Noddy awfully weird in some ways.
Dahl, good one, Hil. Thanks.
Some recent-ish books for a 6-year-old who is reading above grade level:
The Giggler Treatment, Roddy Doyle. Though pooh figures prominently in the story line, I love this story of what the Giggler do to get revenge.
Speaking of pooh... the Captain Underpants series are so amazingly funny, but gross with lots of fart jokes. Very appealling to my 6-year-old friend Evan.
Midnight for Charlie Bone by Jenny Nemmo. It's a bit like a Harry Potter knockoff, but I find them immensely satisfying. I love Charlie Bone and his ability to "hear pictures." It's no scarier than HP 1 & 2.
Everything on a Waffle, by Polly Horvath. The protagonist's parents are lost at sea and she is taken in by her well meaning, but flakey uncle.
And you know what Evan loves? Junie B. Jones. Those are pretty easy books, but he loves them so much.