For your Aberration Hunter

High-Charisma Paladins are good, if you go that route I recommend you pick up a few levels of Topaz Guardian-you'll gain more Will Save bonus. a Special Diadem that gives you bonuses to AC, and the Smite Aberrations ability (in LoM, I'll post any class on here your interested in that you don't have access to)

If you play any Spellcaster I highly suggest that you take levels of the Keepers of the Cerulean Sign PrC-it gives you the d6 hit dice (a welcome change for wizards or Sorcerers), doesn't hurt your Casting at all, and has some sweet Antiaberration stuff, including an insta-kill ability at 10th level, and even has good Skill Progression (for some reason)
You should also take the Aberration Banemagic feat, granting you extra damage against aberrations

Not much for the good ol' rouge, except the Darkrunner class-trades all the "I'm a rouge, s I'm the god of reflex saves" for Some good Underground stuff. Only problem is that it needs Darkvision to get in, so only Half-Orc, Goblin, and Dwarfs are gonna get in...

I heavily recommend a Druid-as much or more than a Cleric-and for that Druid I recommend the Abolisher (especially if you already have a Keeper)they get some interesting Stuff

You guys play Psionics? If so I recommend Wilder, (even though you get less Powers, you get better BAB and some anti-touch abilities, Wild Surge will help beat Power Resistance and Saves)
Do not waste your precious Powers on stuff that requires Will Saves-Abberations (especially Flayers, and your probably going to fight a lot of them) have good Will Saves. Don't Waste your time

For a Ranger I advise you to take the Wild Talent Feat and Waste no time getting in to the Illithid Slayer PrC (XPH) REALLY good against Illithids (hence the name). I also recommend going down the path of Archery, just to be sure. Many Abberations have a couple of AMAZING melee combat stuffs (The Flayer's Extract Brains, Umber Hulk's Massive Strength, Aboleth's Mucus Cloud, etc.)

Spells: Detect Abberation is a must (2nd level spell, Detects all Aberrations within 60ft.) and Invoke the Cerulian Sign (3rd for everyone except Rangers and Druids, who get it as a 2nd-great for fighting a bunch of weak enemies-Like Grell!) nature's Purity (Druid 3, good for damage, no saving throw) Mind Blank is good, Conjuration Damage Spells are good because they don't have SR (for some reason), Evokations with Reflex Saves, b/c many Aberrs suck at 'em.

Psionics: Anything that gives a Fortitude, Reflex, or No saves, increases your Will Saves, or Drains Power Points

Skills and Feats: Get Grapple Checks. I can offer a couple of feats for this. If this isn't an option, BY THE GODS AT LEAST PUT RANKS IN ESCAPE ARTIST!!!!!!!!!! If you don't the First Flayer you find will just eat your brains.

Don't overlook Iron Will and Greater Fortitude, sure, they may have less Pizzaz and Flare when looking at Power Attack and Cleave, but you'll be upset when you fail your Save by 2 and become the Flayer's or Beholder's Thrall, or Get turned to Dust by an Eye Ray, Get enslavedor turned to that weird thing Aboleths can turn you into with their Mucus by an Aboleth, or Die from Massive Damage from an Umber Hulk w / levels of Barbarian. Man, that would suck.

I'll be able to give you more individual feats and stuff, I just need the classes you guys are playing. And Races, while your at it.