CIRCUIT AWESOMENESS CircuitLab, interactive circuit design / learning.
Upverter how to publish circuits / schematics online and share them.
Conventional flow vs electron flow. Diodes look backwards in the latter. Documented at AllAboutCircuits
Light dimmers are usually implemented using a triac, but they can buzz too over time. nice design article. Another option seems to be a mosfet too, but not sure how to drive it.
Most are nice frontends onto SPICE. LTSpice, Qucs, and Electric are recommended for up to mid-level projects.