Feat: Jungle Veteran. Allows you to always act during the surprise round. No prerequisites. Not an effect you usually see available at such a low cost.
Feat: Spawn of the Dark Prince. Not only does it give a whopping +10 to Bluff checks, it's also an Abyssal Heritor feat, which means you can get it from embrace the dark chaos without even having to do the full shuffle.
Spells: Boccob's rolling cloud. It's the same damage as fireball, but it's a cone instead of a spread, and the damage is evenly split between fire, electricity, positive energy, and negative energy, so it still interacts with fire-related stuff like Fiery Spell or Fiery Burst, but it isn't nerfed by one of the most common resistances in the game. Here's the kicker: anyone who fails their Reflex save for half damage also needs to make a Fortitude save or be dazed. Not too bad. "But spreads are easier to aim than cones, and what are the odds of them failing two saves in a row?" you might cry. Well, my friend, I have another underrated alternative for you: shockwave. It deals 1d4/level nonlethal force damage (max 10d4) in a 20 ft. radius, and anyone who fails a Fortitude save is dazed for a round. No energy resistance at all, and you can subdue enemies rather than killing them, and you get a save-or-suck on top of it all.
Spell: Shark bolt. Imagine scorching ray, except instead of flame rays, it's sharks. How cool is that.
Item: Chickens. Did you realize they're only 2 cp? That's 50 chickens for a single gold piece. Do you know how many monsters you can distract by throwing chickens at them? A lot of monsters, that's how many.
Item: Amber amulet of vermin. These things are wildly underpriced for their effect. Only 700 gp to drop a massive scorpion on your enemies' heads? A bargain.
Prestige class: Urban savant. Easy to get into, gives lots of skill points, full casting, and you can peek at the enemy's character sheet. One of the best arcane prestige classes around IMO, but I rarely see it mentioned.
Prestige class: Thrall of Fraz-Urb'luu. Have you seen that 10th level ability? It lets you turn an illusion into reality. That's free magic items with Nystul's magic aura right there. Plus it adds a bunch of illusion spells to your spell list, or, if you're a warlock, even better, gives them to you as SLAs, which means no material components for simulacrum and ice assassin.