I used 100 EZ Lessons for my son, and he loved it. It is set up so that you pretty much just read the instructions aloud, so it's very easy to teach. Readers graduate very quickly to reading stories on their own. I got mine used for ~$10.

My daughter did NOT like 100 EZ Lessons,though, so I got her Alphaphonics. Alphaphonics seems daunting at first because it's just lists of words and sometimes lists of sentences. There are no stories. The words are arranged into groups by sound, and you basically say, "this letter makes this sound, now you try." There is an abbreviated teachers manual in the back, but it's difficult to flip back and forth. This book does take some getting used to, BUT it works SO MUCH BETTER for a reader who is having a difficult time. I really don't know what the magic is, but it works. I got mine used for ~$15.