http://www.preschoolbystormie.com/ : This is the best and most organized website I've found. Stormie has all her ideas organized and laid out in a monthly curiculum by theme. I base a lot of my themes and monthly planning off her ideas. It makes planning really easy!
http://www.childfun.com/ : This site is organized by theme and has a bunch of great ideas as well.
http://www.everythingpreschool.com/ : This is one of my other favorite websites as well. They have their site broken down by themes as well, and has their ideas under each theme further broken down by music, science, etc. They have coloring pages and even have some already developed lesson plans.
http://www.preschoolrock.com/ : I haven't looked at this website very deep, but the few ideas I've seen on it are great.
Books:
Read, Sing, and Play Along: Children's Lullaby Songs. I orginally bought this book for the lullaby cd's, but it has a bunch of activity worksheets and has every story (Jack and the Beanstalk, The Little Red Hen, Etc.) and lots of fingerplays, as well as other theme extending ideas to go with each. I plan on using this a lot more next year.
The Toddler's Busy Book: This particular book is designed for 1 1/2 -3 year olds, but I found a few ideas in there for some fun reinforcement activities. There is also a Preschooler's Busy Book by the same author and others that she has put out. (I may have to extend my collection!)
And I have a whole slew of other books and things that I pull ideas from. I hope that helps. If you know of any other great websites, books or cd's, please share! Also, I'm looking for a good CD with all the favorite songs on it: Hokey Pokey, Chicken Dance, etc., so if you know if one, please let me know! Enjoy!