When my kids were little I found a great site with free printables for Pre-K. If I was rating this site on only the PreK-K stuff I would give it a solid **** but I am rating the overall site.
So the site has free printable worksheets; which is always a plus! They claim to cover worksheets for Pre-K to 5th grade.
You can check out their whole site here.
But if you want to skip to the good stuff, my favorite is the Itsy Bitsy Books. They are a bit tricky to put together the first time but after you figure that part out they are awesome! My son loved them when he was little. The are simple enough kiddos can memorize them and learn the letter sounds at the same time.
We were also a fan of the pre-printing pages.
One thing you will notice is the pages are very simple so if you have one that is distracted by all the other things on the page these are perfect. However, my kiddos found them to be a bit boring. The have a range of subjects including Math, Science, Language Arts, History, and more. Personally, we only used them for Pre-K through K stuff in the Language arts section because I thought the other sections were too simplified.
However, check them out and let me know what you think.