I have lost some of the mortar between the blocks in my foundation. What do I need to do to fix the cracks it is causing. Can you suggest a product?

First, I think I'd check those blocks for settling. Can you see the inside and outside of the wall? Is the cracking due to stress/settling? Is the drainage adequate? There are several products available. Check your local home improvement store (Lowes/HomeDepot), some will not only advise you which to select, but some provide in-store seminars, too.

If it isn't to noticeable id just use some sacrete or quickcrete, unless you want to try your hand at mixing masons mortar and sand,
Other wise id just get a trial and redo the mortar where it needs