I get lots of requests for book/series recommendations--from kids and adults. Makes sense--after all, I am a K-5 librarian. That said, I struggle with my answer. Book choice can be very personal and one child's "best book ever!" may easily be another child's "what's the big deal?". That said, there are some books and series that are consistently popular with the kids at my school. With this in mind, I thought I'd put together a list of these with links to websites that give more information about each. Grade levels mentioned are merely suggestions based on observations--know your readers.
For 3rd through 5th graders:
Jeff Kinney's Diary of a Wimpy Kid series
Erin Hunter's Warrior series
Rick Riordan's Percy Jackson series
Jeff Smith's Bone graphic novels
Dav Pilkey's Captain Underpants series
Shel Silverstein's Where the Sidewalk Ends and other poetry
On a daily basis, I get numerous requests for books, any books,on specific topics--often more requests than I have books. These popular topics include: how-to-draw, origami, world records (especially the Guinness World record books), the Titanic, I Spy, dinosaurs, and jokes & riddles.
For Kindergarten through 2nd graders:
Nick Bruel's Bad Kitty and Poor Puppy
Alyssa Capucilli's Biscuit books
Dav Pilkey's Kat Kong and Dogzilla
Mary Pope Osborne's Magic Tree House series. An added benefit for this series is the availability of the non-fiction research guides to match the various topics.
Barbara Park's Junie B. Jones series