Secondary professions for a Ranger

Ranger/Warrior

 * Energy-based melee attacks are affected by Expertise, thus allowing a Ranger to use them at reduced cost.
 * Rampage as One provides quick adrenaline gain when combined with skills from the line of Hammer Mastery. These rangers are often referred to as "Bunny-Thumpers," because of the way they run when carrying a hammer.

Ranger/Monk

 * Mending Touch is useful for condition removal and Purge Signet is useful for multi-hex removal.
 * Rangers have efficient self heals and should not invest in Healing Prayers.
 * Resurrection skills such as Rebirth are useful on primary rangers, because rangers tend to have better survivability than other professions and can save a party from a near Party-wipe.

Ranger/Necromancer

 * The "Touch Ranger" takes advantage of Expertise's effect on touch-range skills. This, combined with ranger defensive stances and speed boosts, makes a powerful build with decent armor ignoring damage and potent healing.

Ranger/Mesmer

 * Echo chains can be useful when trapping.
 * Fevered Dreams and Epidemic can be used to spread AoE conditions.
 * Greater Conflagration and Winter combine well with Mantra of Frost to reduce physical and elemental damage to almost nothing.

Ranger/Elementalist

 * Elementalist spells such as Conjure Flame can be combined with Barrage to deal extra damage.
 * Kindle Arrows may also be coupled with Conjure Flame to deal a substantial amount of damage without the necessity of a fiery bowstring.
 * The Earth Magic or Water Magic lines of the Elementalist can grant the ranger extra armor.
 * Ward spells could be useful as a last line-of-defense when foes close in.

Ranger/Assassin

 * Signet of Malice can be an effective condition removal skill for Rangers that focus on spreading conditions of their own.
 * Expertise lowers energy cost of dagger attacks, making skills like Repeating Strike more maintainable. This can also be used to make longer use of Moebius Strike and Death Blossom.

Ranger/Ritualist

 * Weapon Spells such as Splinter Weapon, Nightmare Weapon and Brutal Weapon can work well with a bow. They combine with Barrage and Dual Shot to create a potent damage spike.
 * Binding Rituals are affected by expertise, though Primary Ritualists are often better Spirit Spammers.
 * Access to one of the Ritualist's reusable resurrection skills (Death Pact Signet or Flesh of My Flesh).

Ranger/Paragon

 * Energy-based spear attacks are affected by Expertise, thus allowing a Ranger to use them at reduced cost.
 * Song of Concentration can be used to set traps in the middle of battle.

Ranger/Dervish

 * Rangers can successfully use this build to spread conditions more efficiently. By using the elite Ebon Dust Aura on an ebon bow, in addition to the other condition causing enchantments the dervish has to offer, this ranger has the ability to cause serious damage and provide successful defense against warriors and assassins.
 * Expertise can be used to reduce the energy cost of scythe skills and combined with Ranger stances such as Escape or Lightning Reflexes. This makes a fast running or fast hitting, hard to damage and multi-hitting Ranger.