Are there any spells for mages to perform sneak attacks?

According to a post in this thread, magic attacks are all noticeable, but don't get a sneak bonus anyways.

Casting spells make noise and they don't got a sneak bonus anyways.

There is a spell to allow quiet casting, as mentioned in a different post:

You can sneak+cast with Quiet Casting, yes. However, doing so, with most spells gives away your position almost immediately. And there is no damage bonus for sneak attack spells.

However, as also noted in the post, this will most likely give away your position and defeat the entire purpose of sneaking to begin with.

The Illusion school allows you to one-shot, at range, opponents who are in a group.

Let that sink in.

You cast a spell and sit back while his friends take him out. It's not instantaneous, but it's very sneaky.

If you want to play as a stealthy mage, you need to take special care to keep your Illusion skill level & perk purchases on par with the level of your opponents. See the 2nd half of this Answer for a guide.

Open by casting Fury/Frenzy/Mayhem (Dual cast if required) into a group of opponents. Their reaction? "Hey, I saw a spell flash over there, but there's a madman right here trying to kill me!" Take advantage of the the distraction to relocate in case they come searching.

Repeat as required until you're left with a single opponent. Feel free to take him down with the Destruction/Conjuration/Restoration spells of your choice. The Impact perk can be very useful for controlling a single strong opponent and, past the novice level, destruction spells work well at range. Yeh, bows or better crossbows make a decent 1st shot on your last opponent, but after a while your bow skill levels should fall behind your destruction skill levels and the bow will become less attractive.

Spell sounds don't carry too far. If you're using Lydia as your active follower, they're more likely to hear the sounds from her heavy armor than your spells. So the Quiet Casting perk is most useful when casting a spell around the corner from a foe or near Falmer. This might be most useful when casting Muffle, or an AoE Fury effect in tight quarters. Invisibility might be helpful to re-acquire your stealth status.

The main disadvantage of this approach is that these spells are limited by the level of your opponent and your opponents will, generally, level with you. As such, purchase the following perks before the relevant milestones:

• Out of the box, Fury is good to L6. The Adept level AoE spell Frenzy is good to L14, but it's Mana cost should be prohibitive for quite a while and the book won't hit the loot tables 'till XP L23 or appear in stores before you gain Illusion L40.
• At Illusion 20, purchase Illusion Dual Casting. This gives you a Dual Cast version of Fury that is good to L13, and, if you can afford it, DC Frenzy will be good up to L30.
• Soon after Illusion 20 you'll also want to pick up Animage as a prerequisite to later perks. Other than Mammoths (Animage DC Frenzy), most animals that appear in groups won't be a challenge for your casting abilities.
• At Illusion 40, purchase Kindred Mage before blowing past the L13 limit on DC Fury. Let's be honest, this is the hardest of these milestones to hit before it becomes a problem. Gratuitous abuse of Muffle should help. At this point your numbers are:
  • Fury: L16
  • Frenzy: L24
  • DC Fury: L35
  • DC Frenzy: L52 - Note: You can stop spending Perk points here if you don't mind the Mana costs of DC Frenzy. Darned few opponents level beyond 45.
• At Illusion 50, you can purchase Adept Illusion making the mana cost of Frenzy less insane. You can also purchase Quiet Casting so you can summon Bound Daggers almost directly behind your victim.
• At Illusion 70, purchase Rage for the following targets:
  • Fury: L28
  • Frenzy: L36
  • Mayhem: L47 - Note: Probably the most powerful "Fury" effect for which you'll ever find a use, unless you're casting at very long range or you want to start using Illusion in vampire dens. If you've completed the Black Book: Waking Dreams you may even want to respec without Illusion Dual Casting.
  • DC Fury: L61
  • DC Frenzy: L79
• At Illusion 90, you can extend your abilities to influence the minds of undead, daedra, and automations with Master of the Mind. Target levels for these non-person/non-animal beings are:
  • Fury: 18
  • Frenzy: 26
  • Mayhem: 37
  • DC Fury: 39
  • DC Frenzy: 57

Let's be honest, these spells are for picking off the low hanging fruit of groups, so you are unlikely to want to target anything over 45. Seriously, stop asking Tolfdir for trouble.