I guess it would be wise to explain myself on the quests
For silithus, you turn in the texts to get your rep up to around revered
From here you can turn in the items listed for quests,
normally you have to go through a long process to get these items, but the items are farmable/tradeable/AHable
so you can literally just get one and turn it in for a quick 12k xp
For STV
Go to ZG and just start killing, there are 9 coins, you need one of each (i wont name them, but once you get 9 different coins your good), and of course the one bijou
Now go to the ZG island which is in the northwest part of the zone, past the basilisks, pasts the headhunters, its on a little island
There you will be able to turn in 4 quests, 3 coin quests and 1 bijou netting about 40k xp for about the time it takes to go from org to grom (5min?)
Enjoy!
*Edit* Coin quests no longer give XP but Bijou still does, silly blizz