They're quite good. The books go from pre-readers up through high-school level reading, IIRC.
ISBN: 0471288896
Amazon has a couple of copies of the first volume with more expected. There are at least 7 volumes in all.
It's hard to go wrong with Dr. Seuss too.
I think the main thing is find books that are fun and interesting.
Good luck!
Cheers,
Scott.