I’m a great fan of the open-source vector-drawing software Inkscape. Although I don’t have that many figures in my papers (or notes), I’ve found it quite accessible and easy to use to produce high-quality results. And just yesterday, as I wanted to add a picture to my notes on expander graphs, I learnt of a very nice new feature: from version 0.48 onward, one can select a special option when saving a drawing as PDF that creates an auxiliary LaTeX file, which can then be incorporated in the source file (using the standard \input command) and which contains (and processes) all the text found in the drawing. This makes it very easy to add arbitrary LaTeX (math) formulas with Inkscape.
For example, the SVG file
produces a PDF file
and a LaTeX file, and when the latter is inserted, the document reveals the beautiful picture