Originally Posted by
jsn55
This is all good to know ... I already have the DLAmEx and am looking for non-AmEx solutions. .
Zorak is correct. You don't say which DL AMEX card you have but obtaining the next level up (such as Gold to Platinum) allows you to earn the initial sign-up bonuses that get you to your described earning goal in the time it takes you to make sufficient purchases (typically $3000 in spending) during the first 90 days.
Other ideas:
1) Book an air/hotel package via Delta Vacations and earn up to a 70,000 bonus Skymiles. Use Promo Code: SMBONUS Miles earned depends on the amount of your package.
2)
https://www.skymilesshopping.com/p/extra-rewards.htm page shows extra bonus offers through shopping at that portal. For instance, a subscription to Motley Fool earns 9000 SkyMiles.