Through April 30 you can get a 20% discount on Sky Club (Delta/Northwest) one-year and three-year club memberships. Simply use promo code DSC20 when making the purchase. If you don’t have an American Express Platinum card, this is about as good of a deal as you’ll get for lounge access at any airline. For example, a one-year membership for a Platinum Medallion is now $240, while it’s a mere $576 for a three-year Platinum Medallion membership. At the same time United raises their prices to $400 for top tiers, while still not offering free drinks….