As of this posting, High Gravity Homebrew is giving bonus gift certificates based on how large of a gift certificate you purchase.
$45 gets you a $50 Gift Certificate
$90 gets you a $100 Gift Certificate
$900 gets you a $1000 Gift Certificate
Since you can use gift cards on anything, this amounts to a back-door sitewide discount.
Also at High Gravity: Hands on Review: Wort Hog Turnkey Electric e-BIAB System! | Bootleg Biology at High Gravity