Secondary professions for a Warrior

Warrior/Ranger

 * The Ranger line offers a few alternative IAS skills.
 * Apply Poison can be helpful with Cyclone Axe, Hundred Blades or Whirlwind Attack to spread poison among foes.
 * Troll Unguent is a powerful self heal, but requires hefty investment in Wilderness Survival.
 * Flourish can be used to spam expensive Bow Attacks, Focused Shot is particularly useful as the last attack before Flourish.

Warrior/Monk

 * The condition and hex removal skills of the Monk close a critical gap in the warrior skill line. Skills such as Mending Touch, Purge Signet and Empathic Removal are good utility skills.
 * Despite the popularity, Healing Prayers skills are much less effective than Healing Signet, and should be avoided. This is especially true of Mending, which can cripple a Warrior's already slow energy regeneration for a mere 6 Health per second gain.
 * Balthazar's Spirit increases adrenaline gain, and provides a net energy gain if the Warrior takes more than 1 hit per 3 seconds.
 * Succor can allow a Warrior who does not use energy to provide allies with additional energy regeneration.

Warrior/Necromancer

 * The most common usage of the Necromancer secondary is for condition removal via Plague Touch.
 * Rend Enchantments can be used as an enchantment removal.

Warrior/Mesmer

 * Wise use of Physical Resistance, Elemental Resistance or elemental mantras can add additional survivability to solo or tanking builds.
 * Hex Breaker is often useful as a cancel stance and for hex prevention.
 * Web of Disruption can be used as an interrupt in a build with little energy skills.

Warrior/Elementalist

 * Shock can be used as a snare and interrupt, however exhaustion will certainly be felt with a Warrior's low energy pool.
 * Grasping Earth can be used as a AoE snare to keep groups of enemies from kiting as efficiently.
 * The conjure skills, such as Conjure Frost can provide additional damage when wielding an elemental weapon for a very small investment of energy.

Warrior/Assassin

 * The Assassin has a wide range of snares and shadow steps that can serve a Warrior well. Shadow Prison is an outstanding skill in this vein.
 * Signet of Malice can provide free condition removal.
 * Dash is an excellent speed boost that also serves as a quickly recharging cancel stance for Frenzy.
 * Death's Charge is useful for closing distance in battle, but take care not to outrun your party's support.
 * Disrupting Dagger is a useful interrupt which cannot be blocked or miss.
 * Flourish or Warrior's Endurance can be used to spam expensive Dagger attacks.

Warrior/Ritualist

 * Sparing use of Weapon skills can benefit a Warrior; Splinter Weapon can be combined with Triple Chop or Hundred Blades. Ritualist primaries, however, far outclass Warriors at spamming weapon spells.

Warrior/Paragon

 * Remedy Signet may be used with no attribute points for a quick, energy-free method of condition removal.
 * Battle Rage can be used to spam adrenal Spear Attacks, and Flourish can be used to spam Energy-based Spear Attacks.

Warrior/Dervish

 * A Strength and Scythe Mastery based build can be effective, with Flourish or Warrior's Endurance covering the cost of Scythe Attacks.
 * Many Scythe Mastery skills are general-purpose Melee Attacks (i.e. Rending Sweep) rather than weapon-specific skills, which allows them to be used with axes, hammers, and swords.
 * A scythe can work in a Steady Stance/Drunken Blow/Desperation Blow build.
 * Rending Touch can be used as an enchant removal.