My favorite workbooks are by Brain Quest. Their workbooks contain more than the usual math & language arts. They have science, social studies, creative writing, etc all in one book. Another product I've used with my kids are the Brain Quest cards which are available for ages 2-13 years old as well a variety of topics like Black History, For the Car, America, etc. I usually buy Brain Quest supplies at Costco ... Look in the book section for their workbooks & cards ... I saw some cards there today. :o)
HERE is another mom's review of the Brain Quest cards.
Not only do these cards have great educational value, but they also help with bonding and one-on-one time. I love to take my little ones, sit them right in my lap, and work on the cards with them while they are cuddled up close.