sscalc
SUB Shellcode Calculator - written while studying for the OSCE.
This isn't intended to fully automate the encoding process, but should provide as a supplementary tool to validate manual encoding during the course. You can paste your target bytes into the yellow boxes at the top, and then calculate the desired 2 or 3 pass sequence of opcodes to use in your exploits. If there are bad bytes listed in the output, you can easily change them in the calculator and produce new companion bytes to result in the same target bytes.
Everything here should be available in a single self-contained HTML file.
The most important thing I've learned from this project: Arithmatic in Javascript is terrible. :)