talk the dm into allowing you the hidden talent alternate class feature for soulknives.
legacy champion will advance your soulknife levels with full class features.
pyro is a fun addition to soulknife, though it doesn't add directly to class features.
there is no particular rule against manifesting two of your mind blades, taking the appropriate action to do so for each, twf with the feat that allows you to shape your mind blade to specific weapons, take scimitar and dervish levels.
or just twf with your mind blade and a pyro's fire lash. or take variant kinetic for different types of energy damage.
there are dragon feats which also boost the mind blade abilities. assuming you can get that past the dm.
psy-war for a couple of feats and useful powers isn't all bad, especially if you get the hidden talent acf mentioned above. note that you can pick any power with hidden talent, iirc.
illumine soul is decent and stacks with soulknife nicely.
i know you didn't want soulbow, but some features do stack retroactively onto the mind blade, plus granting decent range for a level or two. might be worth a look. plus the mention that core soulknives effectively get full bab with mindblade.
kalashtar race has nice racial sub levels with soulknife.
hmmmm. that's all i can think of for now. ^^
edit: oh yeah, mau-jehe can either stack with or function as a second mind blade simultaneously with your existing one. works even better if you decide to take the legacy champion prestige. combine with the pathfinder or athas soulknife for maximum effect.