Psionicist (VG Class)  

Psionicist
Type	Caster
Races	High Elf, Thestran, Dark Elf, Gnome, Kurashasa, Mordebi, Qaliathari, Goblin, Kojani, Half Elf, Raki

The Psionicist is the master of the psionic energies, having abilities to give the power to blast foes with mental energy, create large area destructive spells, stop a foe's heart and even enter opponents minds, rendering them paralyzed. The Psionicist uses powers to destroy the enemy ranks and to protect and augment his allies. The Psionicist is a poor melee combatant, but his vast mental powers more than make up for it. -Sigil

Basically a Psionicist is a damage dealer who also has a wide variety of utilities ranging from crowd control to buffs. While Vanguard officially has no crowd control class per se, Psionicist is likely the best class at crowd control.

More information on this class can be found at VGPsi.