The theme for my A-Z compilation will be, naturally enough, PSIONIC MONSTERS!
Aboleths are sweet, meaning, they have lots of potential.
Although they have the bodies of giant fishes, they are clearly related to Mind Flayers, as they are also highly intelligent, lawful evil, psionic slavers, with four tentacles and slimy skin, who prefer to live deep underground.
Fitting them in the average campaign is not easy, as they are not really a random-encounter kind-of-monster, so they more or less demand their own underdark-related milieu. If you aren't creating a whole milieu for them, they could at least be fit into a good "underground lake" scenario.
I am in the process of fleshing out an underdark war scenario in which they will play a major role. Something along the lines of Aboleth vs Mind Flayer vs Kracken, with proxy human/morlock/drow armies, that kind of thing.
Psionic ability: 250
attacks: Ego Whip, Id Insinuation, Psychic Crush
defenses: Thought Shield, Intellect Fortress, Tower of Iron Will
Special powers: illusions, enslavement
The illusion and enslavement powers aren't really spelled out in Appendix I of the 1e PH. Is enslavement equivalent to Domination? Or more like Hypnosis? DM call on that one, the way it is described, it actually sounds like Telepathic Projection to me. DM decision-making called for on that one.
Also, you have to get creative on the illusion-making thing, as there is no such psionic power listed in Appendix I.
I would also think they would be great candidates for Telepathy, as they would otherwise have no way to communicate with their slaves.
If you really want to throw your players for a loop, give 'em the Shape Alteration feature as well, so they would walk around as men. Or even Mind Flayers! The whole point of an underdark milieu of battling psionic slavers would be to really screw with your players minds! Aboleths, with their illusion-making ability, would be perfect for that.