Two weeks ago, I wrote a post on why new shaman should choose enhancement. Enhancement was my first love in this game and the reason I was finally able to break my streak of level 20 to 40 alts and level to 70 in The Burning Crusade. First loves aren't everything, though. (There's a reason the American divorce rate is something around 40%). This post is for my second love and the other option for leveling shaman. This is why you should choose an elemental shaman.
Elemental shaman are ranged casters. Lightning Bolt will be your primary damage spell, particularly at low levels. Earth Shock is a very good burst damage ability when you're very low-level but doesn't scale as well as Lightning Bolt. You'll want to use it for the first 15 to 20 levels, and then forego using it in lieu of another Lightning Bolt until you reach the Fulmination talent. Thunderstorm is also incredible damage at low levels and possibly more useful as a damage spell than a knockback spell until you level up and mobs start to be an actual threat. Lava Burst becomes available at level 34. Lava Burst is the lynchpin of the elemental rotation, and you should get used to keeping Flame Shock up on a target, Lava Bursting whenever it is available and Lightning Bolting in between.