Smashwords book page, just use the coupon code SSW50 at checkout to get half off. The ebooks are on all formats including mobi (for Kindle), epub, pdf, and many more. You can even download them as a text file if you're weird. No one's ever done that yet. Offer ends July 31.
The only books not on sale are those in my Toxic World post-apocalyptic series. Those are exclusive to Amazon so Kindle Unlimited subscribers can read them for free (even though Amazon still pays me, nice deal).