Classes to add for a second playthrough with my group

[Kafana]

I'm using the 3.5 system and so far we've only been using the three core rule books (I did use a few monsters from MM 3 (creepy stuff there) for a specific encounter, but that really doesn't affect anything).

I'm looking into expanding my game. I've read half of the PHB 2 book (the four new classes, the new feats and spells) and I'll soon take the DMG 2 to see about some new items (though items aren't a big problem, since there was little focus on them in the first playthrough).

Anyway, since I liked Neverwinter Nights 2, I decided to open up Complete Arcane and look at the warlock class, and after seeing that it's pretty much the same as in the game I decided to include my favorite class for the summer campaign as well.

So, that's the Warlock, Beguiler, Dragon Shaman, Duskblade, Knight. Now, I have two questions.
1) If I port the warlock from complete campaign, do I have to port anything else, e.g. spells for wizards, sorcerers and prestige classes? I don't want to buff those classes, especially since the sorcerer and wizard are already overpowered, in my opinion.
2) What other class from the Completes can I import? I am looking for something completely different, like the warlock is with his evocations. Something that can't be found in the 11 core classes, the 5 I've mentioned, and preferably in none of the core prestige classes. Not necessarily strong, but interesting and original.

[Waker]

1) If I port the warlock from complete campaign, do I have to port anything else, e.g. spells for wizards, sorcerers and prestige classes? I don't want to buff those classes, especially since the sorcerer and wizard are already overpowered, in my opinion.
No, not really. You can port over stuff from CArc or CMag when bringing in Warlock invocations, but there is nothing that compels you to do so. For reference the three biggest sources for Warlock invocations are Complete Arcane, Complete Mage and Dragon Magic.

2) What other class from the Completes can I import? I am looking for something completely different, like the warlock is with his evocations. Something that can't be found in the 11 core classes, the 5 I've mentioned, and preferably in none of the core prestige classes. Not necessarily strong, but interesting and original.
Mechanically speaking, the classes that come from the Complete series that do something new is fairly limited. Scouts from Complete Adventurer use an attack similar to Sneak Attack that relies on movement rather than the target being flat-footed or flanked. Spellthieves from the same book allow a character to steal spells and SLAs from a target. Ninjas also from CAdv, have a Ki mechanic that lets them use a few neat powers, though the class itself is weak. Hexblades from Complete Warrior have a fairly ineffective Curse attack that debuffs enemies.
If you are looking for new mechanics and classes, you might want to check out Tome of Battle, Magic of Incarnum, Binder from Tome of Magic and Factotum from Dungeonscape.

[Kafana]

Could you list a specific class or two?

[Waker]

Scout (CAdv)- A mix of ranger and rogue. Their unique mechanic is Skirmish, dealing extra damage and gaining ac when they move in a round.
Spellthief(CAdv)- A semi-caster rogue. Their unique mechanic allows them to steal spells, SLAs, and energy resistance against targets hit by their sneak attack.
Ninja (CAdv)- A mix of monk and rogue. In addition to a strictly worse sneak attack, they can utilize ki to become invisible, gain a miss chance, strike incorporeal...
Warblade (ToB)- one of the three initiator classes. Often touted as the "Fighter fix", the warblade has a diverse range of maneuvers and skills.
Swordsage (ToB)- Another initiator. Has access to the widest range of skills and techniques. "Monk fix".
Crusader (ToB)- Last initiator. Excellent tank, "Paladin fix".
Binder(ToM)- Allows spirits from outside of reality to possess you in exchange for super powers. Binding mechanic allows a character to change powers daily.
Incarnate (MoI)- One of the meldshapers. Utilizes an energy called Incarnum to shape their spell equivalent around their bodies for all-day buffs/equipment.
Totemist(MoI)- Another meldshaper. Similar to Incarnate, but with a nature theme.
Factotum (DS)- An everyman adventurer. Unique mechanic gives them Inspiration points to spend every encounter, granting them bonuses on skills, saves and attacks.