I have a Fun Preschool Time scheduled with my little ones, ages 2 and 4, each morning. I don't use a set curriculum; I use a variety of inexpensive workbooks and materials I have printed from different websites.
Here are a few of my favorite sites for preschool materials.
Easy Fun School has a TON of great printables. The site's main page has a lot of resources for older school ages, too, including Unit Studies.
Everything Preschool has some great thematic units, projects, recipes, and bulletin board ideas.
P.E. Central has lesson plans for preschoolers geared toward improved balance, coordination, and physical skill.
Preschool Education offers many thematic units and art project ideas.
Letter of the Week is one of my all-time favorites. I have used this program for several years. Mrs. Lybbert, a homeschool mom, has developed a complete line of curriculm for young homeschoolers that is wonderful. She includes links for books, poems, composers, crafts, etc. Disclaimer: Mrs. Lybbert has links to some Mormon sites which I DO NOT endorse!
Toddlers and preschoolers are little sponges that just soak up learning-- it you make it fun! If you work with preschoolers in your home or at church, I hope that these sites will be a help to you!