I just bought Glencoe World History (like new) and student resources (new) on CD, and all told spent around $60. I also bought "Get Ready! for Social Studies" books, which are really clearly presented and excellent. I feel like we're set for a couple of years on social studies with these.
EPGY might be good for math; I haven't tried it but checked out the sample videos recently. ALEKS is decent, but I don't know how to stack it against EPGY. DS6 likes Singapore Math, and it lends itself well to acceleration. For math enrichment, try the usual suspects: Life of Fred, Ed Zaccaro Challenge Math, Singapore Challenging Word Problems / Intensive Practice, Mathematics Enhancement Programme (which is free and also a stand-alone curriculum in its own right), Sunshine Math (free), etc.
I know that Michael Clay Thompson is highly regarded for language arts instruction among homeschoolers, but I don't have it myself and am still weighing our options for next year. Our current public school uses 6+1 Traits (for which Evan Moor puts out decent workbooks) and John Collins for writing instruction, and in my opinion they're decent.
For science, I would stay away from the religious curriculums (Apologia, Bob Jones University, etc.) as they tend to be written from a young earth creationist viewpoint, which would only serve to confuse a child and present an obstacle to pursuing a later interest in science. Building Foundations of Science Understanding is often recommended as a secular option, but again I am currently weighing our options and can't make much of a recommendation.
