After Darkshore, I went to Ashenvale but got bored quickly by the area, monsters and quests. So, I hopped on the zeppelin to the east and did some grinding in my favorite Horde area Silverpine Forest and Hillsbrad Foothills until about level 25 (hearth location Southshore). To make it less boring, I also did some grinding in the Wetlands in between (hearth location Menethil Harbour). After 25, I went to Duskwood (hearth location Darkshire) which is a fantastic leveling ground if you are a fan of creepy, spooky areas like Silverpine Forest. Lots of Skeletons, Worgen, Ghouls and the like in rotten farms and graveyards there. Raven Hill has an awesome atmosphere (beware the single patrolling level 35 elite boss near Forlorn Rowe and the catacombs/cemetries). The quests you can get in Darkshire are nicely done and get you quickly to level 30. After 30, I went back to Hillsbrad (Southshore) and started grinding through the Yetis (Darrow Hill, Growless Cave up to the Alterac areas). This is where I'm now with level 31, almost 32 (just killed the level 36 rare-spawn "Skhowl" there solo with my Night Elf Druid :)). I'm going to do Yetis up to 34 and then Alterac Ogres up to 37 with some visits in the Arathi Highlands (Raptors, Ogres). At 37/38, grinding in Swamp of Sorrows is great until level 40, which is my first goal for now to get that nice Tiger mount. I have to note that I'm a very visual, atmosphere oriented guy who always picks the areas and monsters that fit my personal taste best, so don't consider my tipps the best possible way for a Night Elf :) All of the aforementioned areas, by the way, are also great for an Alliance herbalist/alchemist as the herbs there allow you to level up these professions very quickly (Kingsblood, Life Root, Khadgar's, Steelbloom, Goldthorn, Winter's Bite etc).
"Man only plays when in the full meaning of the word he is a man, and he is only completely a man when he plays." -- Friedrich von Schiller