I didn't feel it was necessary to spend much money on purchasing a curriculum for preschool. The majority of the learning that takes place in the early years will come through play and exploration. However, here are some of the resources I use for ideas:
Joyful Heart Rhyming Times for 3's - Bible and Rhyme: This is a free online curriculum for preschoolers put together by a very dedicated and hardworking homeschooling mom. I'm not sure how she has had the time to put all this together and make it available for the rest of us...but, God bless her! I am following the outline of this curriculum mainly for Bible, but I am also using many ideas she has for other areas as well.
Other Resources for Bible: The Singing Bible, Pray and Play Bible, The Bible in Felt Stories, several different children's story Bibles, etc. ...I am blessed to have a mother that has worked in children's ministry her whole life. She has made all of her resources available for me
We are also using bits and pieces of: Hooked onPhonics, Letter of the Week (this is another free online curriculum), Hooked on Math, The Letter People (this is hard to find...I happened to come across it in a garage sale), First Steps to Reading, and some of my own ideas added in.