This company offers several affordable options for online curriculum. You can purchase e-textbooks for core subjects in individual grade levels. (These appear a bit dry, but would be a good "spine" to start with.) They also offer two structured online curriculum systems that appear to be flexible and allow a fair amount of control by the parent. All of these options include subscriptions to the Brittanica School Online reference tool and a discount for an online homeschool planning system.
Saturday Grab Bag
Printable curriculum materials for preschool through second grade levels.
Thursday History/Social Studies
This website from the Government Publishing Office has resources for learning about the US govern
The name of this site says it all!
Tuesday Language Arts
This company provides programs for beginning reading and math learning.
This company publishes three books for helping elementary learners explore science.
Self-paced, online courses for learning coding.