We love the K12 curriculum and are starting our third year this fall (www.k12.com). It is pricey if you purchase it on your own, but if you are in a state with a Virtual Academy charter school they will pay for K12. There are minimal compliance requirements with a charter, such as, in CA, turning in quarterly work samples and participating in state testing. The other families in the charter can provide a good support group of similar families which might be helpful to someone starting out homeschooling. Just letting you know this may be an option for you to consider, depending on whether or not you wish to homeschool independently or would be interested in a charter.
My parents did not use a homeschool curriculum when the homeschooled us (I guess I should say "do not use," because, while I am in college, I still have sibblings being homeschooled). Rather, they checked out books from our local library (my mom actually went over the 99 book limit at our local library once) and had us read those.
Some of the more major text books, such as those in high school, they purchased such as Biology, Physical Science, Chemistry, Geometry, Algebra 1, Algebra 2, and Advanced Mathematics (which is basically Pre-Calculus). The only discipline for which they ever really stuck to one group was math, for which we used Saxon Algebra 1 and up.
I have not worked with curricula for any grade level above 3rd grade (yet.) I have heard great things about ACE and KONOS.
Best of luck.