Choose two:
-Seducer: Easiest to craft. With the changes to resource management in Morrowind, this set has become a good starting option for lower level players on the Magicka side. Eventually you will want to replace this with something else though, as you lose too much damage at higher CP and can sustain with other sets. Does not come in Jewellery!
-Julianos: Craftable fairly early on (though you do need Orsinium DLC). Staple set for Magicka builds. Use this paired with a second 5pc set. Does not come in Jewellery!
-Scathing Mage: Although not too flash on single target, still very powerful on Magicka Sorcerers in multi target, as the set is one of the few that hasn't been beaten to death with a nerf hammer and still offers 500 spell damage.
-Netch's Touch: This set had one of the bonus stats changed, and now the set is currently the strongest performing sets on non-Pet Sorcerers. MAKE SURE you use duo-lightning staves if you are using this set.
-Mother's Sorrow: The increase to Critical Ratings this set received bumped the effectiveness of the set up quite dramatically. If you don't have access to Netch's Touch or Infallible Aether, this is a good option to go for until you can get those sets.
-Infallible Aether: The bonus damage to heavy attacks from this set is still very good, along with the extra crit added in Horns of the Reach. Wouldn't use this over something like Netch or Julianos though.

"What about Burning Spellweave?": Morrowind changes reduced the spell damage bonus and proc chance of this set, and besides Dragonknights this set is a shadow of its former self on all classes. Still good on a Sorc if you run Blockade with a fire Staff, but it is no longer a priority.

"What about Spinners Garments?": Your spell penetration even in solo content reaches maximum without this set, so it is completely overkill. It is a strong option for PvP though.

"What about Twice Born Star?": Once the big King of Damage Dealing Trial Runners everywhere, now just the sand beneath Julianos' shadow. Don't run this set from here onwards, its just not worth the effort. It deals less damage than Julianos in both non and pro-Warhorn environments, and needs more traits to learn.

1pc Monster Set:
-Iceheart: 4% Critical Rating from having just one piece of this, preferred for damage.
-Molag Kena: More Spell Damage. I would recommend this on a Mother's Sorrow build, to get just that extra little bit of punch.
-Shadowrend/Chokethorn: Extra sustain. If you want more regen, this is an option.
-Domihous: Both Magicka and Stamina for the 1 Piece. Do not doubt the importance of this, the extra Stam can mean the difference in breaking free when you need to, especially in vMA and vDSA

Infused+Nirnhoned Weapons: Sharpened has been brought down. Infused with Shock/Fire enchants on front with Nirn+Weapon damage on back are the way to go now. Here's the important part: Which enchant element on front. If your group has several people running the Asylum Destro Staff you'll want fire, as there is now no reason to run Shock and proc Concussed. If not, Shock is still preferred.

Lightning+Lightning Staff: Running Off Balance with Blockade of Storms is highly recommended for Mag Sorcs. Using Shock Heavy Attacks on front bar is also important for damage while sustaining.