PaintCC Triode and Pentode Modeling Software
One of the very few tools that can model pentodes. Runs in Java, and you must follow the installation and use instructions
exactly for it to work. Dmitry has indicated that some updates to make it more user friendly will follow soon.
Another excellent tool that can capture curves for both diodes and triodes. Requires TCL to be installed.
Follow the directions exactly!
Federico Scarpa's Triode Tube Model Pages
Here is a new collection of commonly and not so commonly used tube models for spice (mcap), new additions almost daily.
These are based on the Norman Koren Model.