Check out Kolbe Academy, too — I can vouch for them! http://www.kolbe.org
Kolbe Academy is the largest Catholic curriculum provider of the “Classical Education” type, while Seton is “Scholastic Education.” There’s also Our Lady of Victory, whose emphasis is “Traditionalist.” All of these are excellent.
I’m inclined to “unschooling,” so we use a wide variety of Catholic and non-Catholic curriculum, depending on what the children ask for and what’s on the used-book rack at our local homeschool curriculum store.