First-School.ws - This website is great. They have so many different resources and they are all free. All you have to do is print.
DLTK- Has some fun crafts to go along with the letters you will be teaching your preschooler.
Also, the dollar store usually has some preschool activity books and posters. I purchased an "ABC" and number poster each from the dollar store and they work great. I have them on the wall where I do preschool and every day we repeat the "abc"'s and the numbers together. The activity books work great too. They have them for letter writing, number writing, colors, shapes, sounds, etc.