Here is a listing of my current favorites for preschool aged children. I just came across the first one today. It has LOTS of really great printable's which I will be using for my son's age 3 preschool this coming school year.
www.kidslearningstation.com - has lots of great printables for all preschool stages.
www. starfall.com - ultimately the best interactive site out there for little ones. what a GREAT teaching tool!
www.chasingcheerios.blogspot.com - this blog has great crafty ideas for kids. this would be great for those who use more of a waldorf or Charlotte Mason style of learning. lots of hands on fun:)
http://www.letteroftheweek.com/preschool_age_3.html - this is a great way to really reinforce each letter of the alphabet.
Have fun teaching your little one:)