so warrior is out of the mix
rogues, hunters, warlocks, priests and paladins seem pretty common from my battlegroup.
so druid, shaman, and mage all seem like pretty good choices
from personal experiences, i've had a blast playing on an FC mage and FC druid.
i would definately note that mages are one of the most dynamic DPS classes, if not the most dynamic, at 39. a plethora of spells at your disposal, but they really have to be timed well in order to be effective. not a class for someone who isn't very skilled, unless you're going to make an arcane mage FC (which is incredibly easy to play
)
druids are very dynamic in that they can choose from many different specs. feral spec does somewhat poor dps but is very good for survivability as well as just being a nuisance to your target because of the speed and feral charge. druids can also FC pretty well as either 0/30/0 or 0/13/17. balance spec provides you with very high heals and a glass cannon that can output incredible single target dps with wrath as well as burst with starfire and multitarget dps with dots. resto druids are very good burst healers.
shamans are incredibly underplayed at 39. they are kind of dynamic like druids only in a different way. they have many totems at their disposal such as grounding totem and they have all the shocks which allows them to CC, dps, and interrupt targets. they also have heals and ranged casting spells, although they are a bit weaker than other classes at that. if you decide to you can go enhance and basically swing a slow speed weapon and hope for huge procs. resto is a very good utility healer. enhance provides for a very dynamic dps class. whichever way you spec or gear your shaman it will always have utility, and kind of be like the jack of all trades.