I'm sorry if this is not the proper forum to ask this question but I wonder if there will eventually be a geometry HF (I understand this is likely), an adv. algebra and trigonomy, a pre-calculus, calculus, linear algebra and matrix theory, ....
Head First Geometry will be out later this year (2009). As for the others, that really depends on how the math and science books currently out do. If they sell really well, we'll definitely keep investing in that area. If they don't... well, supply and demand :-)
At this point, the only in-progress math/science title is Geometry. Honestly, we could sign several more, but we need to see how the current titles do before committing more resources to additional titles.
Series Editor, Head First