There are 16 magic-user spells of 8th level in AD&D, up from 8 in OD&D. All 8 OD&D spells have made the transition to AD&D at the same level. One spell - maze - was originally 9th level.
Antipathy/Sympathy: This spell imbues an object or an area with an aura that either attracts or repels certain creatures. It can be set up to affect a specific creature type (hill giant, red dragon, orc, etc.), or a specific alignment. If set up to repel, all relevant creatures need to make a saving throw to remain in the area, but if they do remain they suffer some loss of Dexterity. If it is set to attract, all relevant creatures need to make a saving throw or they'll feel an overwhelming urge to remain in the area, or to grasp the object. Even if they make the save, they'll need to make another in 1-6 turns to prevent themselves from going back.
Bigby's Clenched Fist: Creates a fist that the caster can use to strike opponents with. It always hits, with its effect dependent on a d20 roll, ranging from 1-6 damage to 4-24 damage and stunning for 3 rounds. It has the same number of hp as the caster. The material component is a leather glove, and a device made of four rings that sounds a lot like brass knuckles.
There's a bit of an inconsistency in this spell that I'm not sure about. It says that no other spell-casting can be done while the fist is in effect, but later it says that it can be used with any of the other Bigby's Hand spells. So can those spells be cast and no others? Or can the Clenched Fist also be made to perform the actions of those earlier spells? I might be inclined to allow the latter.
Clone: This spell creates an exact duplicate of a person that grows over 2-8 months. The clone and original know of each other's existence, and will seek to destroy the other. If this hasn't been achieved within a week, there's a 95% chance that one will go insane (most probably the clone), and a 5% chance that both will go mad and commit suicide. The material component is a piece of flesh from the original, and the clone will possess the attributes of the original from when that flesh was taken.
The OD&D spell was much the same, but with that spell it was inevitable that clone and original would both go insane. It also spells out that the spell is useful for being brought back from destruction, provided a lump of flesh and appropriate instructions are left behind with the right people.
Glassteel: Gives a small amount of glass or crystal (10 lb./level) the strength of steel, with a permanent duration. It material components are a piece of glass and a piece of steel.
Incendiary Cloud: Creates a cloud that burst into flame after a number of rounds. On the third round it deals damage of 1/2 hit point per level, and in the 4th round it deals 1 hp per level, before dropping back to 1/2. After the 5th round, it is simply an obscuring cloud. It requires an existing fire source, and affects an area 100 times that of the fire.
I'm tempted to criticise this as yet another high-level spell that doesn't deal a whole lot of damage, but that area effect is potentially massive - under the right conditions, you could wipe out an army with this spell.
Mass Charm: This works like charm monster, but it can affect a number of creatures with Hit Dice totalling up to twice that of the caster. The spell is potent, and all targets suffer a -2 penalty to their saves.
In OD&D, the spell affected a flat 30 "levels" of monsters, with "level" here presumably referring to Hit Dice. It had a range of 12", as opposed to 1/2"/level in AD&D.
Maze: The target of this spell is doomed to wander in an extradimensional maze of force planes, for a time determined by their Intelligence. In a lovely mythological touch, Minotaurs are immune to this spell.
This spell was 9th level in OD&D. It was much the same, but it's duration based on Intelligence had less tiers. On the whole the AD&D spell lasts longer - a creature of average Intelligence in OD&D will be trapped as long as someone with an Int of 17 in AD&D. There was nothing mentioned in OD&D about minotaurs.
Mind Blank: The recipient of this spell is protected from all forms of mind-reading and also cannot be discovered by scrying devices and spells. This also includes psionics, and even wishes, but doesn't extend to powerful deities.
The OD&D spell is the same, albeit with a much shorter list of powers that it protects from. It doesn't specify protection from psionics, or mention deities at all.
Monster Summoning VI: This summons 1 or 2 monsters of 6th level. Once more taking a look at the tables from Supplement I: Greyhawk shows some exceedingly nasty stuff: titans, golems, balrogs, beholders, liches, purple worms.
The OD&D spell only summoned a single 6th level monster.
Otto's Irresistible Dance: The target of the spell must dance uncontrollably, suffering a -4 AC penalty, losing all shield bonuses, and automatically failing all saving throws. Note that this spell also has no save, although it does require a touch attack. Still, if it works it gives you 2-5 rounds to throw spells at a target for which it will get no saving throw, which seems pretty deadly to me.
From what I can gather, Otto was an NPC magic-user that lived on the second level of Castle Greyhawk, who was subdued by various PCs and became the henchman of Robilar.
Permanency: This spell can be used to make another permanent, but there's a finite list of spells (twenty in all) that it can affect. Some of the better examples are infravision, protection from normal missiles, and enlarge. Any spell that is made permanent on the caster drains him of 1 point of Constitution.
The OD&D version was known as permanent spell, and had far more leeway in interpretation. It was recommended that there be a limit of one permanent spell per object, and two per creature, but otherwise it's left up to the DM. It specifically mentions levitate, haste, fly, and water breathing, all of which are not allowable in AD&D.
Polymorph Any Object: This spell can be used to transform any creature or object into anything else, with the duration determined by the difference between the two forms. If the forms are closely related it will be permanent, but otherwise it varies. It's barely been changed from the OD&D version.
Power Word, Blind: This spell affects up to100 hp worth of creatures, striking them blind with no saving throw. The spell lasts longer the less hp worth of creatures it affects.
The OD&D version of the spell worked on a single creature of up to 80 hit points, and its blindness effect lasted for days rather than rounds.
Serten's Spell Immunity: The caster can grant resistance to various spells to a number of targets, one per 4 levels of the caster. It lasts for 16 rounds, but this is spread out between all recipients. The spells it grants resistance to (in the form of a saving throw bonus) are mostly mind-affecting: charm, suggestion, fear, hold, geas, quest, etc. The material components are diamond dust sprinkled over each target, and a diamond in the possession of each target as well.
Serten was a cleric played by Ernie Gygax, which raises the question: why is an 8th level magic-user spell named for a cleric? He most certainly didn't develop it himself.
Symbol: This spell creates a magic rune that has one of a number of effects when triggered: death (killing up to 80 hp worth of creatures); discord (loud bickering); fear; hopelessness (the targets are dejected and basically helpless); insanity (targets act randomly); pain (-2 dexterity and -4 attacks); sleep; and stunning. It has a material component of 5,000gp worth of powdered opal and diamond.
The OD&D version of the spell has less effects (fear, discord, sleep, stunning, insanity, death). The first three of those have no limit on the number affected. The latter three start talking about "level points", which isn't entirely clear. If it refers to Hit Dice, then the "death" function kills 75 Hit Dice worth of creatures, which is pretty full on. If it refers to hit points, then the power levels are somewhat comparable.
Trap the Soul: The target's soul is trapped in a specially prepared gem worth 1,000gp per Hit Dice of the target. The true name of the target is required for this spell to work. It can be cast directly on the target (in which case they get magic resistance and a saving throw), or it can be applied to a "trigger object" that will trap the target when it is handled. The soul is trapped forever, or until the gem is broken. If the creature trapped is a powerful extraplanar being, the person releasing them may demand a service of some sort. In a great touch, this can apply to high-level PCs who are so trapped outside of the Prime Material Plane.