This might be deemed to not be MR-related, but as an MRer I'm always looking for easy ways to bring down CPM/EQM, and I've found the following way to reliably work.

NW e-certs can be bought on craigslist.org for $8 at any time and give the following discounts:

$25 - fare of $75-$199
$50 - fare of $200-$299
$75 - fare of $300-$399
$100-fare of $400 and up

You will receive the discount code and a document number through e-mail (no shipping anything).

This is just for those that didn't know...