The unit studies that we use either come from Five in a Row or Homeschoolshare. Homeschoolshare is a free website where dozens of ladies have come together to write units to share with other homeschooling families. Besides book units, there are animal studies and book report ideas.
Each spring, in order to get more units submitted to be able to use, they host what's called The Blast. There are prizes given to the best written units in certain categories. For the last 2 years, I have participated and written some units, and I will participate again this year. What units will I write? Hmmm...you'll have to wait and see.
For more information on homeschoolshare, you can click on the link above, or on my sidebar on the right.