Secondary professions for a Warrior

Warrior/Ranger

 * The Ranger line offers a few alternative IAS skills.

Warrior/Monk

 * Skills such as Mending, which has a small return for a high cost of attribute points and Orison of Healing, which is a mediocre heal, should be avoided.
 * Mending Touch is a useful form of condition removal, even with little or no attribute point investment.

Warrior/Necromancer

 * The most common usage of the Necromancer secondary is for condition removal via Plague Touch.

Warrior/Mesmer

 * Wise use of Physical Resistance, Elemental Resistance or elemental mantras can add additional survivability to solo or tanking builds.

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 an 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.

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

 * Warriors and Paragons have very little Synergy.

Warrior/Dervish

 * A scythe can work in a Steady Stance/Drunken Blow/Desperation Blow build.
 * 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.
 * Rending Touch can be used as an enchant removal.
 * Pious Haste can be used as a cancel-stance for Frenzy.