It sounds like you're looking for a restoration (healing) spec. The classes capable of healing are druid, monk, paladin, priest, and shaman. Racially there aren't a lot of significant differences, though specific races can only play certain classes. (Alliance races are listed below as well, though the original question was about Horde)
- Druid (Horde: tauren, troll; Alliance: night elf, worgen) - limited to leather armor; tree form (cooldown ability) increases healing throughput; good profession choices: skinning/leatherworking, herbalism/(inscription or alchemy), mining/jewelcrafting
- Monk (any except Horde: goblin; Alliance: worgen) - limited to leather armor; use brews and teas as the primary basis of skills; similar professions to druid (I've never played a monk healer, so can't really address the specifics...)
- Paladin (Horde: blood elf, tauren; Alliance: draenei, dwarf, human) - can train to use plate armor at level 40(?), limited to mail previously; some people think they are limited to single-target (tank) healing, but do have some raid utility too; professions: any of the combinations mentioned above, or mining/blacksmithing
- Priest (Horde: any except orc; Alliance: any) - limited to cloth armor; best professions: tailoring/enchanting or herbalism/alchemy
- Shaman (Horde: goblin, orc, pandaren, tauren, troll; Alliance: draenei, dwarf, pandaren) - can train to use mail armor at level 40, limited to leather previously; can also use shields; in addition to direct healing spells, also have totems that provide passive effects and healing; professions: similar to paladin
For all, you can learn first aid, cooking and fishing as secondary professions that will come in handy.
Note that resto is much easier to level as primary spec now that you get access to the LFD tool at level 15. And, they're in big enough demand that you shouldn't normally have queue times that are very long.
ETA: Cataclysm/Mists updates
Update for Patch 4.0.6!
Leatherworking is now exactly as good as blacksmithing / enchanting / alchemy / inscription. Pick Jewelcrafting if you need that 1 extra stat, but the rest are totally a wash.
Original Answer
Jewelcrafting can give up to +81 to a primary Stat, whereas enchanting / blacksmithing / inscription etc. only give +80. (Exceedingly minor difference.)
Also worth looking into is Leatherworking, which offers unique arms-slot enchants that are unique in that they provide a primary stat bonus (such as strength) otherwise unobtainable as an enchantment in that slot.
In general, the gathering professions provide less useful benefits than the secondary professions, a possible exception being Mining, which provides health. (Strength is a better damage increaser than both crit rating from skinning or an activated haste+heal from herbalism).
So the bleeding edge optimization would indicate Leatherworking and Jewelcrafting as the best, in terms of pure +stats. Mining / Jewelcrafting is easier to level, and the bonus health from Mining is not wasted during the period before (if) you switch it for leatherworking.
Beginning with Wrath, and developed to completion in Cataclysm, class is largely meaningless when looking at profession bonuses. The core primary stats of Intellect / Spirit / Strength / Agility are usually all available within a single profession (if they're present at all), making class choice largely irrelevant.*
Even Tailoring isn't useless for melee characters, as it provides a +AP cloak enchant (though its proc-based benefit compared to simply passive +strength is debatable)
Best Answer
The mind flay ability that the Tentacle of the Old Ones casts has a 40 yard range, although like most channelled abilities it only needs to be within that range at the start of the cast, and requires quite a bit more range to break the channel. I would expect that constantly attempting to outrange the tentacle would not be an ideal solution.
The tentacles can also be targeted and have 15k health and can be killed. They are classed as 'guardians' so you could enable health bars for enemy guardians to make them more visible. This means that you should also be able to use a /target macro specifically for targeting tentacles as a counter for this ability.