Secondary professions for an Assassin

Assassin/Warrior
Due to the high dagger attack speed, this combination gains a lot of adrenaline, so it's possible to use adrenaline skills to great affect. Skills such as Rush or "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 and Burst of Aggression. Burst of Aggression can be particularly useful, as it has no negative drawback for its speed boost other than the loss of adrenaline, which Assassins do not often use.

Example Builds:
 * Build:A/W BoA Assassin

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.

Example Builds:
 * Build:A/R Critical Barrager
 * Build:A/R Solo Rajazan's Fervor Farmer

Assassin/Elementalist
Assassins can benefit from elementalist spells much the same way warriors do. the Conjour line of spells, as well as point blank skills like Shock and Aftershock are particularly effective.

Earth Magic also provides some excellent defensive skills.

Example Builds:
 * Build:A/E Falling Shocker
 * Build:A/E Signet Spiker

Assassin/Mesmer
The Mesmer skill Blackout can be used while all of your attack skills are recharging without penalty, and can also be employed in combination with Temple Strike to further lock down a foe.

The Assassin Mesmer is excellent at running, especially in pairs. with a 20% enchantment item Shadow Form coupled with Arcane Echo and Arcane Mimicry can produce an unimpeadable team.

Example Builds:
 * Build:A/Me Solo Sin

Assassin/Monk
The Protection Prayers skill Mending Touch is a good spell to remove risky conditions.

Example Builds:
 * Build:A/Mo Black Widow

Assassin/Necromancer
Curses hex spells can be used to drive many attack chains.

Assassin/Ritualist
This combo yields minimal benefit for an Assassin primary.

Assassin/Paragon
This combo yields minimal benefit for an Assassin primary.

Assassin/Dervish
In the same fashion as the Build:A/R Critical Barrager, 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.

Example Builds:
 * Build:A/D Disciple of Death