#1
This is more of an exploit than a hack.

There's an Amazon workaround that lets you get 20% off pretty much every product via their Wedding Registry program.

How it works:

1. Go to this site  and click on the link to sign up for a free Amazon Wedding Registry

2. Complete the signup form, and set your wedding date for tomorrow

3. Wait until tomorrow. You'll get 20% off on any items remaining on your list.

This works for pretty much anything... TVs, video games, dishes, you name it... they do exclude a small handful of specific products, but in my experience this list is short.