Here's an interesting one if you have some Wyndham points in your account, but you really would rather have United miles. Through August 31st, you can redeem your Wyndham points for double United miles. With this promotion instead of redeeming 6,000 Wyndham points for just 1,200 United miles, you will get 2,400 United miles.
Just login to your United miles account and click on Mileage Plus Program, Earn Miles.
You will see the promotion about halfway down the page and if you click on it, United will give you a drop-down menu of how many Wyndham points can be redeemed for United miles.
The minimum is 6,000 Wyndham points.
You can probably get more value out of Wyndham points by booking Wyndham hotels, however, if you have a trip in mind and need United miles, then this might be a good hack for you.