Well, it looks like those short freebies from Charles River Editors, a.k.a. the "Vook" virtual textbook people, are beginning to be offered again in the Kindle store.
Currently there's 4 shown up so far. I don't know if that's it for the current batch, or more are slated to trickle in later, but here's a
search link which should pull them up by publisher and show only the genuinely free ones. It turns out they're geo-restricted to the US, which is why my original search failed when I copy-pasted it to another browser to check.
In case any show up in other regions, here's a
keyword search on the publisher sorted low-to-high.
Watch out, since there are some which are only "free" if you use one of the Amazon Prime monthly lends on it.