I hesitate to post....As a mother of 4 avid readers, who are much older than seemingly 99% of the board users... I do have some advice.
All four of my kids have tested gifted, and were/are still very advanced readers in high school. (The 3 that are hs age or older are placing out or finishing 2+ yrs of college before graduating hs). They have read beyond college level for years.

All four have issues with processing skills, etc....twice exceptional. Reading could have been difficult/unfun for a couple of them, easy, yet all four of them list as their favorite thing to do as reading many times over. Punishing them is to take away a book they have started. And their favorite store is the local Border's, Barnes and Noble, thrift store, and univ bookstores.
As an example, my 10th grade son I've written on other posts read every single fiction book in his school library last year, include classics like original English translation of The Count of Monte Cristo. He read many non-fiction books, too. He was reading piles of books a week, and the librarian commented how he never entered any of the reading reward programs. She rewarded him through ordering books early, so he'd have them when they were new, and ordering special interest books.
Never, ever have I used incentives for any of my kids for schoolwork or reading.
Why? Because it doesn't work long term.

Here's a couple research links I found. Other research that will contradict is ultimately given/funded by the makers of AR, Pizza Hut, In N Out, etc...you just have to dig to prove it.

http://www.alfiekohn.org/teaching/readingincentives.htm

http://www.pscholtes.com/pscholtes/articles/incentiveprogramsareineffective.cfm

It is basic psychology - based on Skinner. (extrinsic vs. intrinsic motivation).
But to explain why I have seen almost every single eager friend/parent quell their child's love for reading, I offer you this...
It is like veggies. If they know they have to be bribed because they are good for them, they won't eat them without the bribe...even if they feel like it tastes ok. Why eat something if you can hold out and get a treat for it or feel you "deserve" a treat for it from past experience?

My advice for avid readers, who love reading more than anything, that ultimately helps with writing, comprehension, and independent learning is to:
1) Read to them...always. Even if it's a short article when they are older. They love sitting and cuddling with a parent reading, and discussing it. As they get older, pass around the books to everyone and discuss...in the car, at dinner/breakfast, in the store, whenever. Include Dad. (He reads far more than me these days).
2) Have them listen to stories on CD/tape or at storytelling festivals. My kids always liked Jim Weiss, but they also liked Hank the Cowdog, and some of the other unpredictable ones. When they want to read above their level, (I had a kid who was trying to read DeLaires Greek Mythology and struggled with the names), see if there is a recorded version so they can follow along with their finger, if they choose.
3) Give them a dictionary, and teach them how to use it. My kids stick post-it notes in their books and look up words they don't know. This was taught by a teacher at school. Vocabulary = comprehension, especially if they connect the affixes. Comprehension helps them analyze deeper and make inferences, which makes reading more enjoyable.
4) Provide only books that are worthy of their time. Learn about books/authors and quirky publishers. Also, don't make them feel they have to finish every book.
5) Take them to the movie or musical of a book they have read or you have read together. We just did this with "Pride and Prejudice." It was amazing. We loved the music and thought the play really stuck to the book, making us love it even more. Also, author signings are great!
6) Teach them how to choose a book that is the right reading level. They will read more and progress quicker that way. Don't push them to a higher level. They will get there!
7) Discuss the differences between movie and book versions. What was your fav part in the book? the movie? Why? Why do you think they left that character out? What did you not like? etc. Share your opinions, too.
8) Treat books with respect. Show them how to use them, to wash their hands, to never, ever allow a book on the floor, to place it properly on the shelf/nightstand and keep food/drinks away.
9) Take them to the library/bookstore. Check out books with a holiday/birthday/season theme. Read the ones you buy every year as a family...especially Christmas. Making books as a meaningful tradition.
10) Every once in a while (not too often - have them read the whole thing) treat them to pick a magazine in the grocery store to read. Ours has a kids' section, but as their interests grew they would pick a scientific one, sports, etc. Teach them how to pick one out (look at the cover stories/thumb through photos), how to find the 'Contents' page, and be sure to look at graphics and captions. If it is overwhelming, guide them to choose from three that you know are reputable. Then if they start hounding you, buy them a subscription as a gift. Make sure it is in their name only. They will be excited getting them in the mail.
11)Limit or throw out the tv. Use the internet (United Streaming is great if you can get a subscription, as well as networks for news). Limit computers, games, etc. while they are young or until they have discovered books.