Here's the latest Top Ten list from wowvault.ign.com
Top Ten Faction vs Faction quotes:

10) Orc -> Human: Human, the other white meat. -- SgtCodeRed
9) Night Elf to Troll: "So who's your stylist?" -- Eatmyarrows
8) Human female to Undead male: "Oh god, I used to date that guy." -- Bloodthroe
7) Gnome to Tauren: Nice knees. -- LotharTu
6) Dwarf armorsmith to a Tauren herbalist..."Who'da thunk it, a cow gettin' a racial bonus for grazing =p" -- Dark_Disciple
5) Gnome > dead Tauren. "Hmmm, you looked a lot tougher on the box." -- raven722
4) Troll to Gnome: My raptor is so old and out of style, how do you build one of those birdies? -- Kaiche-Strega
3) Human > Undead= Hey buddy, Elm Street is that way! -- KDAWG650
2) Gnome to Tauren : Your not mad are you? No? So, you've been tested then? -- Ozzie-SOL

And absolutely the funniest quote :

1) Human -> Undead: Grandpa? -- SgtCodeRed