New editions of Athenian Steel & Spartan Beast are coming! They are also heading back into iBooks, Kobo, and (for the first time) Google Play. During the transition, they'll be unavailable for 1-3 days at Amazon, after which Amazon users who own the old covers will be able to re-purchase the new versions, should they so wish. (The interiors are the same, but your Kindle bookshelf will look much better for it.) If you do wish to upgrade, be sure you're signed up for my newsletter so I can alert you next week when they are reduced to $0.99 & $1.99, respectively.
Spartan Beast's cover has actually already debuted on Amazon in Kindle and paperback. Athenian Steel meanwhile has been using another new, but temporary, Amazon cover which I also think is pretty great:
Stay tuned to this site, Facebook, or (best option) my newsletter for updated retailer links.
Last but not least: Interim and Death to the Witch-Queen! have beautiful new covers, too: