Originally Posted by MrTumnus

(scroll to bottom for changing profession locations)

It's really up to you but here's a few ideas of what you'd be looking at for each secondary:

Core professions
1.) Monk: Self heals and rez spells A good and popular choice for new players or those who like to try soloing or other builds. Spells usually cost between 5 and 15 energy points.
2.) Necromancer:You've played with it a little bit and know a bit of what it's like. You can cast curse spells, raise minions, and you have a few self heals. The upkeep for minions might be expensive manawise as well. However, I believe there exists a build for the R/N that is extremely effective in PvP.
3.) Elementalist: You have powerful spells, but they cost a lot of energy usually (between 10 and 25), some causing exhaustion (temporarily lowers your maximum spell point capability). Expect to frequently be short of energy unless you are good a energy management. Elementalists use glyphs that affect the next relevant spell that you cast, which can be very useful.
4.) Mesmer: I think the best way to use this combination is as a "shutdown" ranger. You can use your interrupting skills as well as those from a mesmer's spell set to effectively shut down enemy spell casters (monks, eles, necros etc.) as you stop their spells from being cast. I think spell cost averages the same as the monk and/or necro.
5.) Warrior: This was the secondary on my first ever character (since retired to some estate north of Tyria on the far side of the Charr Nation). I chose it because I figured that if enemies got too close in range, I could switch to melee weapons and fight like that. The special thing about Warriors is that they possess skills that are adrenaline based, which doesn't require energy to use. This makes them useful in places where energy is almost non-existent or hard to come by (don't worry, you will encounter these places, but they are few and not until much later in the game). Still, adrenaline based attacks are a great way to complement your attack skills that use energy. Warriors also bring with them "shouts" which can give great armour bonuses to the entire team and activate instantly (which means they cannot be interrupted).

Factions professions: These professions require you to have Guild Wars: Factions to access.

6.) Assassin: I'm too familiar with the assassin profession, but from what I know their most interesting non-primary attribute (their primary is critical strikes) is the shadowstep, which allows you to instantly transport to another location. This can be useful if you ever need to escape somewhere, or do some quick melee damage then get out. (I'm not too familiar with this as a secondary if someone else could elaborate that'd be great).
7.) Ritualist: Spirits Spirits Spirits. Ritualists are great support teammates as they can stand in the back (or middle) line of a fight and shoot while providing enhancements through spirits. Rangers also have their own spirits (via nature rituals) so you can quickly add enhancements to the battle. In addition, Ritualists can also cast armour/weapon enhancing spells that give bonuses to their own or allies' weapons.

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8.) Paragon: As a secondary, you will have access to the shouts of the Paragon that motivate and inspire the team. You can wield either a spear or a bow effectively now, both ranged attacks and you can benefit from their calls and self healing abilities.

9.) Dervish: Dervishes are modified versions of Warriors. With access to Dervish attributes you can now wield a scythe, which can hit multiple enemies at once. They also have self healing abilities and enchantments that can enhance your attacks too.

Any of these would probably be a great profession secondary; it just depends on your fighting preference/style. I can switch professions on any of my characters depending on what I want to play, for instance, my Elementalist doesn't use mesmer spells for energy management but wants a pet so I became a ranger secondary. If i wanted self heals for a soloing urge I'd change to a monk secondary. It all depends on what you want to be able to do in conjunction with your primary profession.

Note that the ranger primary attribute lowers the energy cost of all attacks, Rituals, touch skills, and Rangers skills...which applies to all skills you use even if they aren't Ranger skills.

Originally Posted by MrTumnus

Bottom Line: Play what you want.