Although I haven't read it yet, I mentioned back in January a quasi old school E.R.B. style SF novel that has recently come out called Paragaea.
Now, I've discovered, as seen in the link above, that S.M. Stirling is going to publish two novels set in an alternate world where Mars and Venus were terraformed by unknown forces and become the site of Cold War conflict a la A World of Difference.
The Venus-themed book is coming out first in the fall and will be called The Sky People. The other book in the duology will be called In the Halls of the Crimson Kings and will be set on Mars.
I really like Stirling's stuff (The Island in the Sea of Time and Conquistador in specific), so I am quite interested in these forthcoming books.