Trials can't join guilds no
To be honest, in Wrath of the Lich King alot of the emphasis on CC went out of the window in favour of simply zerging everything down with AoE, much to many people's disappointment. The developers HAVE promised however that CC will be alot more important in cataclysm however.
There isn't really a pure CC / buffing class in WoW in the same way as, say, a controller from City of Heroes or a Loremaster in LOTRO
Most of the classes have CC, some are effective at different things. Mages have Polymorph - which is great of humanoids and beasts for example. Warlocks have banish, which s exceptional at CCing demons and elementals but cannot CC anything else.
Rogues have a decent amount of control through their stuns and incapacitate effects (Gouge, cheap shot, kidney shot, sap, blind) and a very powerful movement speed reduction through Crippling poison
Essentially some MMOs have healers, tanks, DPS and controllers
WoW has healers, tanks and DPS, and most of those roles have some form of CC that can be used on various different targets. There is no one class which is specifically focused on CC to the exclusion of much else.
Paladin's are one of the premier buffing / support classes, with their blessings, powerful heals (if specced into Holy) and abilities such as Hand of freedom, which removes roots and snares, and Hand of Protection, which grants temporary immunity to physical damage.
It does sound like a Paladin may have what you are looking for actually. They have 3 talent trees, one turns them into the most effective tank healer in the game, with a small but very potent toolbox of support abilities and heals. One tree turns them into exceptional tanks, easily capable of main tanking the most difficult raid encounters in the game. The final tree turns them into a excellent melee dps class which, although weak in high end PvP at the moment, does excellent dps, and is highly competitive with most of the other damage dealing classes
The melee dps tree gets access to a powerful 1 minute incapacitate effect called Repentance, which is a strong CC ability, while retaining its ability to buff others and utilise spells such as the aforementioned Hand of Freedom and Hand of Protection. They can still off heal too at a pinch! A dps paladin will sacrifice alot of his ability to offheal due to using melee dps plate gear - meaning that they won't have very much mana. They do have some excellent support abilities however, and the best Paladins are the ones who not only master their particular spec, but who also use their support abilities to aid their team mates as well
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