1-ish.
The two front-line fighters in my Eberron campaign are soulknives. I have fond memories of the goofy fun on 1E psionics, skipped 2E, loved 3.0 psionics despite MAD, and think that 2.5 has really got them running spectacularly now. This is my first time as a DM, so I restricted XPH classes to the Soulknife only (at least at first), so that I wasn't *too* overwhelmed.
A warforged soulknife with Adamantine Body is a *beast* of a tank at low levels, especially when backed up by an artificer with Personal Weapon Augmentation: Bane, a crossbow, and very good die rolls. The Lord of Blades and the Order of the Emerald Claw will both be pouring a great amount of resources at neutralizing this new threat...