Secondary professions for an Assassin

Assassin/Warrior

 * Due to the high dagger attack speed, this combination generates lots of adrenaline. Skills such as "Fear Me!" are good examples.
 * Assassins do not have any attack speed enhancing stances, and can thus greatly benefit from Warrior skills such as Flurry.
 * Many assassin skills require daggers, and are useless with other melee weapons.

Assassin/Ranger

 * Barrage damage can be improved with high critical strikes attributes, adding bonus damage to attacks, energy bonus, and effects from skills like Way of Perfection.

Assassin/Elementalist
The knockdown from Shock can drive an attack chain, though it is no longer as popular as other skills such as hexes to drive the attack chain.
 * The Conjure line of enchantments can increase damage with the assassin's high attack rate.

Assassin/Mesmer

 * Use Arcane Echo to chain Shadow Form when running.

Assassin/Monk

 * The Protection Prayers skill Mending Touch is a good spell to remove risky conditions.

Assassin/Necromancer

 * Curses hex spells can be used to drive many attack chains.

Assassin/Ritualist

 * Splinter Weapon works well with Death Blossom.

Assassin/Paragon
This profession combination provides little benefit for an Assassin primary.

Assassin/Dervish

 * The Assassin Dervish can use Critical Strikes to greatly improve the Critical Hit rate with a scythe. *Scythes, having a huge damage range compared to other weapons, provide the highest maximum damage value for critical hits.