Originally I was thinking of making a separate list of boy's and girl's books, but that seemed silly since there can be so much overlap.

Some of the selections here are for strong year 1 readers - they would be suitable for average year 2 readers. This list is basically only generated from books I've seen or been asked about in 2012 (at the moment, anyway).
Easier books
  • Zac Power Test Drive series
  • Zac Power "normal series"
  • Walter the Farting Dog series
  • Secret Seven
  • Selby series
For someone enjoying "Diary of a Wimpy Kid" - this book is listed as Lexile 950. If you Google "books like Diary of a Wimpy Kid", you will find some of the following:
  • Strange Case of Origami Yoda (Lexile 760)
  • Andy Griffith's books "Just Tricking", "Just Crazy" etc.
  • Morris Gleitzman e.g. Deadly
  • Paul Jennings
  • Enid Blyton
  • Winnie the Witch series
  • Roald Dahl
  • Tashi books
And some more notes boosted from various places around the web, including
http://www.guardian.co.uk/books/shortcuts/2012/feb/08/10-books-boost-boys-reading

How to Tame a Dragon series by Cressida Cowell

**Alex Rider** series
**Harry Potter**
Andy Griffiths "What bumosaur is that?"
Septimus Heap series, starting with Magyk
Book of Lies series by James Moloney
Bridge to Terabithia
Narnia series by C.S. Lewis
Golden Compass series
Young Bond Covering similar ground to Alex Rider, Charlie Higson's books – suitable for ages 10 and over
Horrid Henry
Flat Stanley This classic children's book, written in 1964 by Jeff Brown, tells the decidedly surreal tale of a boy named Stanley Lambchop who is flattened in the night by a collapsed pin-board.
Artemis Fowl "This is in the solid nine-12 years category,"
Diary of a Wimpy Kid Boys aged seven and up - but be warned, the kids in these books are not good role models!
Captain Underpants Exuberant fun for younger boys.
The Cherub series Bestselling author Robert Muchamore became the subject of controversy last October, when a north London junior school cancelled his scheduled visit, citing a number of complaints from parents about the challenging subject matter of his books about a group of orphaned teenage spies.
Holes Louis Sachar's award-winning 1998 novel about a 13-year-old boy named Stanley Yelnats, sent to the juvenile detention centre Camp Green Lake after being wrongly accused of stealing a pair of shoes, will appeal to boys of 10 and over.
Michelle Paver Chronicles of Ancient Darkness series: Ghost Hunter, Outcast, Soul Eater and Spirit Walker
Philip Reeve's Mortal Engines trilogy and prequels
Rick Riordan series, e.g. Percy Jackson or Kane Chronicles
Inkheart series
Some classics like The Railway Children, Call of the Wild
Terry Pratchett books

Lemony Snicket books
My Story and Australian story books
Skulduggery Pleasant series - has some violence, definitely for older readers
Bartimaeus series by Jonathon Stroud
Inheritance series for strong readers - some violence in the battle scenes
And of course don't forget graphic novels and audio books are great for students who don't engage well with chapter books.