In this video I show how to use Keynote to draw figures for LaTeX that blend in with the rest of the document. I show how to set the page size, configure fonts, export the figures, and include them in LaTeX.
If you need to include more sophisticated equations in your figures, then the equation editor in Keynote may not be enough. In that case, you may want to produce a PDF with the equation and bring it as a figure into Keynote. There are two convenient ways to generate PDFs of these sort. First, you may use LaTeXiT, which already comes with MacTeX. Second, you may use the standalone document class.