My favorite resource from this publishing company, started by sisters who were teachers and found that music was a great tool for teaching children, is their Scripture memory song CDs. Titled "Scripture Memory Songs" and "Growing in God's Word", both contain great songs that are kid-friendly, fun to learn, and not the annoying style of music most children's music tends to be. These CDs make great gifts.
I also own their Spanish songs CD and workbook, that together teach some basic Spanish vocabulary.
In addition to that, one day I discovered they were having a huge sale on their cassette tapes, and I filled up my online shopping cart with one of each 50 cent tape containing topics everywhere from physics to silly songs. I'm fortunate I have a cassette player from when I was in Jr. High that still works. The girls listen to those in their playroom while they play, and they've picked up quite a bit of info from them.
They offer so much more than what I've mentioned, but these are the things I have personally used. You can check out more by them at their website, http://twinsisters.com/