Dunno if this is a repost, but i just found these out so ill post.
these were all found on molten wow 3.3.5a, so they probably work on other servers
On the On ruby wings quest in northrend the wyrmrest vanquisher you summon can be taken out of the questing area. You do about 15k damage to pvp players, enemies etc.
If you use Hitchhikers hacks you can fly fast and go all around northrend. Ive never been banned using hitchhikers flying hack. There is a 15 minute debuff that despawns the drake, but it seems if you dismount, and remount it restarts the 15 minute timer.
There is also another vehicle which isnt so obvious. The argent canon. I havent had alot of time to perfect this but ill describe it as best as i can.
You get this canon from the "last line of defense" quest. Once you mount this canon i click both mouse buttons to move forward. You may need to use your left or right arrow keys to rotate in a direction. This drops you off the platform the canon is on. Once on the ground you cant fire. It just says you need to be standing... Keep moving until you hit a group of enemies. Once they attack you the canon will move differently and you can now fire. Now you can use your mouse to navigate like you do your character. The only catch is the canon shot explodes the second you fire. You cant aim and fire long distances like the wyrmrest vanquisher. But you get a nice 70k damage attack. just dismount and wait for your mana to recharge, then remount and you can use this 70k damage attack as much as you like. Again I highly suggest using the fly hack via hitchhiker to fly all around northrend. They really hate this vehicle in wintergrasp...
The range is 0 with a radius of like 20 yards so you need to be near your target, the 70k damage attack is like 30 yards. You can easily take out flying players. But it is very important you are at a complete stop when you attack. So fly to your target, stop then attack and it works like a charm.