I made a few simple tweaks.
* Good fort save. Frontliners get that in other classes. Why not the duelist?
* Add int. to AC AND damage. This idea came from another thread.
* Duelist levels stack with and count as fighter levels for qualifying for fighter bonus feats. He may take them at any appropriate feat level.
Too much? Not enough? I don't feel high...
I took the Swashbuckler from Complete Warrior and combined it with the Duelist, and then added some other class features, like Evasion at 9th and Improved Evasion at 17th.