Want to sell my Macbook Air.

eBay or Craigslist are the two most mentioned sites. For pricing, as a starting point, you can check Mac2Sell, eBay (including completed sales), or Amazon for prices of similar models, to get an idea of what you may be able to charge. Then adjust your price to account for condition, configuration, remaining AppleCare coverage (if any), etc.

It's probably not worth selling if you're going to take a big hit on a current gen model.

How long have you had it? Apple has a pretty good return policy, especially if you have had it two weeks or less.

I've never sold a laptop but the first place i'd go to sell is eBay.

Just make sure you include a lot of pictures of the item and include an accurate description of its condition, and you should be fine.

BTW, good choice for the next mac (see my sig)

I would advise against eBay, the "Buyer Protection" they have makes selling expensive products a nightmare. Personally I've had more luck with Amazon