The big problem is that spellcasters don't work well with high ECL races, because you lose out on so many spellcasting levels. Although if everyone in the party is a monster and the DM takes the lack of spellcasting in the party into account, there shouldn't be any problems. You generally get a lot more synergy with the more physical classes. I would be wary of any super-high ECL races in any case.
For example, let's say you want a mind flayer psion (or sorcerer). Mind Flayers have an ECL of 15, so with your party you wouldn't even start off with any class levels. Of course, you can use plane shift, astral projection (which theoretically means you never need subject yourself to physical harm), charm monster, and mind blast at will. But when you gain your first class level you get... some first level spells. That you cast as a first level caster. Doesn't do a whole lot of good for a 16th level character.
So, if you want a spellcaster, use low-ECL races. If you want a combat type, look for low-to-mid-ECL races that maximize your class abilities.
Some races to watch out for:
* Half-ogres are way too good for a +1 ECL race, and you could easily make a devastating melee character (fighter, barbarian, melee cleric, etc.) if you play to its size and strength.
* Pixies get some really powerful spell-like abilities for only being a +5 race, although by 15th level most foes will probably be able to negate its advantages. But even then you still get Otto's Irresistable Dance 1/day if your Charisma is high enough.
* A 15th level Ghaele Celestial can cast spells as a 14th level cleric and gets a whole mess of specials on top of that. Very overpowered.
EDIT: I would probably go for a thri-kreen fighter specialized in multi-weapon fighting.
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