One of my students ask me about electronic circuit diagrams software and free in the internet.
Well, I found some really good stuff.
One software is TinyCAD. You cand found it in sourgeforge website. It's easy to use and free, but only gives a PNG output image.
Diagramly is an interesting schematic website. It bring us a easy way to create diagrams including circuits. You can export in XML, PNG, JPG, and SVG.