Our favorite tools for drawing:

• [[Visio]] for most diagrams
• [[yEd]] for graph-like figures
• draw.io for quick-and-dirty solutions
• [[PowerPoint]] if you would like to reuse the figures in the presentation
• TikZ (for LaTeX-hackers)
• Graphviz for visualizing graphs
• Inkscape for SVG to PDF and SVG to LaTeX conversion