The "Writers' Corner" would be the best place to move these book plugs. Just give them headline tags like NEW or Free.
Keep "Deals, Freebies, and Resources" for member recomendations.
I have gotten free books, like "Soul Identity" by Dennis Batchelder, and bought many others mentioned here.
It seems more of a problem when several authors hop out of a dark place and push their books.
Personally, I wouldn't mind Book & ereader type ads in MR. So long as it is limited and pertinent.