Samhain Publishing (new & reprint romance & horror, some urban fantasy) are offering 30% off for Earth Day using the coupon
EARTH12 (if I've mistyped something, it's advertised on the rotating ad banner at the top of
their website's frontpage) when bought directly from their store (DRM-free MultiFormat bundles).
This will be good until just before midnight EST and will stack on top of their standard 30% off weekly new release and pre-order discounts. Be sure to load up your cart with anything you think you might want before checking out, as it seems that Samhain coupons are single-use only.