Taco Bell is offering half price orders when you order with their mobile app. You can get up to $10 off (so an order can be up to $20).
In order to do this deal, you need to do the following:
This is a fantastic deal that can only be used once per person per week (no word on how long the deal will last, or if it will be extended). Although you can also order through the desktop website, the offer is only available through the app).
Update: This deal has been extended into November. Continue taking advantage of this deal each week for the foreseeable future.