A few months ago I read "Reading Reflex" by Carmen and Geoffrey McGuinness (pub. Penguin).
The authors have designed a reading method (called Phono-Graphix) which is suitable for remediating reading problems (but it can also be used by younger children who are beginning to learn to read). It is a synthetic phonics system (although it doesn't call itself that) and you can teach your child to read yourself using just the material in the book.
It starts with some "diagnostic" tests to find out what the problem is then goes on to explain in a step-by-step way how to teach a child to read. There is also quite a bit of background information on how children learn to read and what is helpful and what is not.
Usually the problem is that the child doesn't know the "sound code" (the 44 sounds that make up the English language), or has difficulty blending and segmenting, e.g. putting c-a-t together to make "cat", breaking "sit" down into s-i-t.
I found it very useful. My ds1 is 4 and I am using mainly JP to teach him to read, but this book was informative because it cuts what you need to teach down to the bare minimum.
There is another thread in the Education section this evening which is about teaching children to read - and links to other threads - but lots of the advice/opinions given there would be helpful for you, I think.
Other websites I've found helpful are syntheticphonic.com - you can email Debbie Hepplewhite personally and she will give you excellent advice. The Reading Reform Foundation is also well worth looking at.
When he is reading a little better, Barrington Stoke is a publisher that produces books for older children - that is with a subject matter that is of interest to older children who have a reading age that is younger than their chronological age. They have a website.
I hope some of that information is helpful to you. I wish you the best of luck. Has your son's teacher suggested anything? I suspect this has been a problem for some time so surely the school has spoken to you about it?