circuitikz
CircuiTikZ TeX/LaTeX package for drawing circuits
...It was born mainly for writing Massimo Redaelli's exercise book and exam sheets for the Elettrotecnica courses at Politecnico di Milano, Italy. He wanted a tool that was easy to use, with a lean syntax, native to LaTeX, and supporting direct PDF output format. circuitikz is included with the most common LaTeX systems, so it should work out of the box. Anyway, the main dependency is on TikZ/PGF, xstring and siunitx.