Plot for Mac OS X
Plot is a tool to visualize numerical data. It has a nice user interface that allows plot-newbies like me to intuitively create complex plots.
LaTeX on Mac OS X
Gerben Wierda provides a survey on TeX on Mac OS X and a TeX distribution based on both TeX Live and teTeX. TeXShop is a LaTeX frontend with a native OS X user interface. Aquamacs is an Emacs distribution for Mac OS X with LaTeX support, that works well together with the DVI/PDF-viewer TeXniscope. Finally, with Graphviz you can layout graphs (not only) to include them in latex documents.