Abberations

[Vhaidara]

If you don't mind Psionics, the Neolithid from Expanded Psionics Handbook is spiffy at Level 15. Give it a normal Psionic Mind Flayer with ride ranks and you could have a freakish Mind Flayer Knight going on.

I feel that doesn't work from a fluff perspective, since my recollection is that neolithids are basically aborted illithids that didn't die and somehow turned into giant megaworm things. But they hate each other, is the point.