Here are some of my favorites, click on the picture to be taken to the page:
All of the Scholastic Success ebooks (Spelling, Vocabulary, Fluency, and Grammar (6th grade))
Great States Quilt Math- a fun math facts and concepts review
Grammar Cop- silly stories to read and then check for grammar
Any of the Literature Circle Guides and Literature Guides (lots of books available: The Cay, Shiloh, Bud Not Buddy, Bridge to Terabithia, From the Mixed Up Files of Mrs. Basil E. Frankweiler, The Giver, Maniac Magee, The View from Saturday, Hatchet, and MORE!)
Standardized Test Skill Builders: Reading- quick read and respond pages. I use these for morning work a few days each week.
Cursive Writing Practice with Inspiring Quotes- another great thing for morning work
I've found several more great books during the $1 sales, and they put some new ones up during each sale, so keep checking their site! I print the really good ones out and put them into folders. You get 3 downloads when you purchase the ebook, so make sure you save it after you open it the first time!