Math: Kitchen Table Math, Cuisinaire Rods, Base Ten Set, Pattern Blocks, a good algebra book (we aren't that far so I have no rec.)
Science: Handbook of Nature Study, a few field guides, perhaps the RSO series
History: SOTW and AG 1-4, Kingfisher or Usborne History Encyclopedia
Language Arts: McGuffey Readers, Blue Book of Grammar, dictionary, thesaurus
A cheap Kindle loaded with the Yesterday's Classics set and as many free classics as I can find
Personal size whiteboard, lined on one size and plenty of dry erase markers.