This is more of a tip than an exploit, but very few know about this.
Magic Dust - Thottbot: World of Warcraft
This stuff is great for twink BG's. Use them sparingly of course, but toss one at someone guarding a flag in WSG or a base in AB, and capture the flag or base scott free. I've also used them in situations where there's 3 or 4 enemies, and sometimes I'll "dust" one of them for 30 secs while I dispatch the other 2 or 3. Use however you like, but like I said, hardly anyone ever uses these so they'll give you a nice edge.