As one of the charter members of the Order of the d30, I've perhaps been a bit remiss in my lack of pimpage for New Big Dragon Games' line of truly outstanding d30-focused products. Of course, this may be partly due to the fact that NBDG went pretty quiet in 2013, but it was a quietude well-deserved, as it was in the service of putting out the d30 Sandbox Companion.
I'd picked up the d30 DM Companion last year and found it excellent, but I have to say that the Sandbox Companion really takes things to a whole new level of inspiration and utility. It's been getting rave reviews and has been sitting at the top of the best-seller lists on DriveThruRPG and RPGNow since its release.
What you may not be aware of, however, is that the company's face in the blogosphere, Save vs. Dragon, has resumed a steady churn of free d30 one-sheets in the wake of the Sandbox Companion's release. Head on over and check 'em out.
Seriously, if you own a d30, there's no reason not to be picking up anything NBDG puts out, free or no.