Over the past couple of weeks, I've been exploring the depths of the TI-Nspire character set and have documented it here in Charmap.tns. This document contains a spreadsheet with detailed information about all 540 useable characters on the TI-Nspire (including some that aren't included in the catalog), along with a program that allows you to use the extra "hidden" symbols in other documents. If you got a TI-Nspire, download it and give it a try!
EDIT: This has been tested to work in System 2.0, 2.1, and 3.0.1. It should be fully compatible with 3.1.