Hi,
If you're a low-income family, here is a tool to find Head Start preschools in your area:
http://eclkc.ohs.acf.hhs.gov/hslc/HeadStartOffices
We enrolled our daughter in preschool for the first time when she was four, and she enjoyed it greatly (and did well in kindergarten and first grade). We chose a play-based preschool co-op (in which parents had to participate), but there are many different types of preschools, including some that focus on academics. Here are some considerations for choosing a preschool that's right for your family:
http://www.education.com/topic/choosing-preschool/
Some preschools also offer scholarships. You can contact potential preschools in your area and ask about their financial assistance offerings, or here's a video about scholarship money for preschool:
http://www.ehow.com/video_4790646_free-scholarship-money-preschool.html
Below are some additional informational resources you may also find helpful. Thanks for asking!