Paragon Surge + spont. caster = cast any spell you want if you have the slot for it on the spot!
If you're not a Sorcerer, you can also spont. call upon the entire Sorcerer spell list at level 11+ thanks to the Eldritch Heritage (Arcane) line. Specifically, using PS to temp. gain Improved EH.
There's a race that has +2 Int/Wis and gets to add 6 spells to their spell list from any other list as long as it is the same "type" (arcane or divine). Which has all sorts of broken combo potential or you can use it to get level 9 spells at 6th level by abusing the 6-level casters' lists.
Wish and Miracle and all the other xp spells now cost gp instead. Which is great already, but then you realize there's a 1st level spell called Blood Money to avoid paying expensive materials/gp costs for spells and can really go to crazy-town.
The Witch gets an at will save or die right from level 1, Slumber. It's Su, so SR can go fuck off, too. It does have some drawbacks ("only" 30 ft range, "only" round/level [so...delay/ready to use it just before an ally adjacent to the foe gets his turn for the coup de grace], it's mind-affecting) but really, it will utterly wreck solo or duo encounters vs. 2/3 the Bestiary. Then at level 10 they get another at will save or die (Ice Tomb) that just outright hoses anything that's not undead or construct.
Wizard gets to cast his prohibited school spells at double slot cost...but who cares for downtime spells, plus wands/scrolls work just fine as-is. Then he can take Opposition Research to eliminate 1 prohibited school. And if he goes for Elemental specialist, he only *has* 1. Or he can go Teleport Conjuror, get all the bonus win spell slots, and get Sudden Shift which is just like 3E's Abrupt Jaunt except Su instead of Sp (awesome!) and swift instead of immediate (aww...).
The Emergency Force Sphere spell is like a higher level (4th) Wings of Cover that can immediate action protect the whole party and is available to more classes than just Sorcerer.
Dazing Spell is utterly broken, it turns any damage spell into a save or lose, and is just disgusting with the right spell/combo. Remind me to link the "Geysermancer" when giantitp's forums are back.
Persistent Spell is also broken, only +2 levels to force 2 saves. Bouncing Spell is only +1 and lets you redirect a save-or-lose that failed to a 2nd target for a retry. Spell Perfection is the ultimate in broken caster shit, it doubles any numerical feat bonuses the chosen spell receives and lets you apply 1 metamagic to it for FREE (can choose a different one each time, but...it's gonna be Quicken, generally).
Guns are completely broken. They hit touch AC ("only" at 1st range increment, as if D&D combats are long distance, and it's easy to make it 2 or even 3 increments if you want). They get to apply ranged power attack, despite a rule specifically saying touch attacks can't get the bonus damage, too. The main gunner class also gets dex to damage, making them single-stat dependent unlike an archer. And guns have high base damage, higher crits than bows, and can be dual wielded if you choose to be a Pistolero or otherwise go with pistols/revolvers (which you should). The ability to full attack power attack touch AC from range with dex to damage and sprinkles on top is "balanced" by making it so the guns might randomly break (first they take a small attack penalty you don't care about and have a higher chance of misfiring again, 2nd misfire it ceases working). Hurray, balance by randomness! Guns and their ammo are also expensive (especially if using paper cartridges to get reloading down to free action), but...only suckers pay base price. A single feat lets you make guns and ammo and such yourself, with no craft check DC to possibly fail or anything and for anywhere between 1/5 to 1/10 (!!!!) market price, because fuck your "1/3 price" crafting rules!
I seriously think a 6 year old could've made more balanced gun rules than paizo did. Oh, did I mention that how broken the guns will be depends on how hard you play "mother, may I?" with the DM? Because the DM chooses the "tech level" of the setting, and the high tech guns are leagues better than the (still good) primitive firearms. They don't recommend a tech level or say what level the rules of other weapons were balanced around, they just leave it up to the DM. Brilliant....
Dust of Sneezing and Choking also remains unchanged from 3E, iirc.