Concept: Build a ganker around "Mass Hysteria" with good single damage and group damage ability. Another way to put it is that I want a ganker that will make other players afraid :)

Sets:
Monster Sets: We want to go heavy for the bonuses. Slimeclaw (Wayrest Sewers I) gives us a little health recovery and a constant 8% bonus to damage all the time. I had a friend tell me Ilabris is another good one, but Grothdar (Vaults of Madness) is better, in my not so humble opinion. Same magicka bonus plus higher damage that procs more often when you use Grothdar.

Armor, weapons and jewelry: Light armor may not be flashy, "I can take a zerg's attacks by myself and wipe them all", but those set and passive bonuses make them all worth it. We'll have 9 slots (5 armor, 1 weapon, 3 jewelry) so we can get one more full set bonus, and up to 2 partial set bonuses. We can go a little tanky here, add to our magicka, add regeneration, or go for spell damage and critical. Never fear, tho, LaLa is here to sort it all out.
Full Sets: Dreamers Mantle maybe isn't a traditional pick, but hear me out; we get a health bonus, when we have minimal health to start with, magicka, which we will need to keep slaughtering our way through Cyrodiil, and a nifty little proc that knocks back enemies if they attack us when we're too low on health. The only downside is that it doesn't do a lot for our damage, it's a purely survivability pick.
Overwhelming Surge is a good alternative pick. 7 or 8 of our 12 skills are class skills, so its enchantment would be proc'ing fairly often, spreading shock damage around the battlefield. Not a lot of people I know invest in shock resistance specifically like they do for fire damage in PvP, so that should be pretty effective. Just beware if you're trying to stealth with it on, a sudden pulse of shock damage is a good way to let enemy players know you're somewhere nearby.
Spinner's Garments max magicka, spell damage, spell penetration
Magnus' Gift and Armor of the Seducer are two crafted sets you can use while you're training, but don't really have anything impressive after you hit vet. True, MG has a slim chance to remove a spell's cost while Seducer has a set reduction to spell cost, but we should have more than enough sustain to keep us going.

Partial Sets: On the other hand, for the last 4 pieces of our equipment, Magnus' Gift gives us magicka regen, max magicka, and spell damage, while Seducer trades spell damage for more regen. Between the 2, I'd go with MG, but that's up to you.
Permafrost, Robes of the Hist max health, max magicka, magicka recovery
Soulshine max magicka, spell crit, spell damage
Wyrd Tree's Blessing. Shadow Dancer's Raiment magicka recovery, spell damage
Shalk Exoskeleton max health, spell crit, spell damage
Arch Mage, Bloodthorn's Touch, Prayer Shawl magicka recovery, spell damage, max magicka
Mother's Sorrow, Treasure Hunter max magicka, spell crit
Necropotence max magicka
Queen's Elegance spell damage, max magicka
Ysgramor's Birthright max health, max magicka, spell damage