We always used A Beka curriculum, and from my own personal experience in using it, as well as the students who have transferred to the public school in which I teach, I have found that their English and mathematics curricula are top-notch. The students read much more literature, both prose and poetry, than in the Glencoe curriculum we use, and their mathematics is generally a full grade ahead of other curricula (two grades ahead of Saxon, which I recommend only for those who consistently fall behind other math curricula or as a summer review).
However, their revisionist history and science curricula leave a lot to be desired. Their American history paints the United States as the "City on the Hill" that was so popular an idea in the seventeenth century, especially with the Massachusetts colonists. It explores the 18th and 19th century revivals in great detail but leaves civil rights nearly untouched. Additionally, it actually makes the point that the conquest of the native peoples was beneficial for them because it brought them out of paganism and introduced them to Christianity.
As for the science curriculum, my chief complaint is with their biology text, which appears to be intentionally stuck in 1850. For example, they teach a two-kingdom taxonomy, Plantae and Animalia. Fungi are all classified as plants, and bacteria are classified either as plants or animals based upon whether they produce chlorophyll. It's not biology alone that is this hopelessly lost, however; even their freshman physical science text is scientifically backward. They devote several pages of the chapter on sound to a pseudo-scientific explanation of how loud rock music damages hearing, and is therefore evil (Even at age 13, I could figure out that Beethoven played at 100 dB would damage hearing just as much).
That's really the only experience I have with home-school materials, but I do know that many people buy the same texts as are used in the public schools. I use Glencoe texts in my classes, and they tend to be well-researched and -written, and not too expensive (about $40-$60 each, and about $10 more for the teacher's guide), and there are pre-written tests or test-making software available. I don't use those, but if the idea of writing a test is not something you relish, use them; they're educationally sound. Of course, there are better texts if you are willing to invest the time and money, and many companies are willing to send free evaluation copies if you are planning to buy at least a classroom set (30 copies). So if you can get a co-op together to all buy the same book for your kids, then it can really be much cheaper. A classroom set with all instructional materials is usually about $1000, so split among 30 families, it's quite economical.