I used 100 EZ with my two oldest (now ages 13 and 10, but they finished the book when they were 5 and 4 yos.)
I followed up with the Explode the Code series, for some phonics practice, and also used the Pathway readers with child #2 (didn't know about them for #1.)
Truth be told, I think the most important thing is daily reading once they are through 100 EZ. Sit down each day and help him/her read a bit of something at his/her level. And then read something to the child yourself, as well. :)
I've got a third girl coming up now, and we're in the middle of 100 EZ. I plan to follow the same plan.