Okay, since there are no really exact descrptions for the other ones, here's some speculation:
O'Neil Colonies and Neyel Warships from The Sundered:
Both are essentially asteroid bases refitted with engines.
Tholian warships from The Sundered:
Since the novel takes place a few years before the Galaxies at War timeframe, the Tholian ships probably are identical to those that Taldren released last month.
Cardassian Akril-class from The Art of the Impossible:
That's already been covered.
Klingon Birok-class strike cruiser from The Art of the Impossible:
As I said before, I picture this as a modification of the Kleev-class XCA from Orion Pirates. Since the Klingon economy didn't have a lot of money to throw around, it would make sense that this was a modification of another design rather than a new ship. So, perhaps the Birok is the XCB?
Romulan Amarcan-class Warbird from Vulcan's Heart, mentioned without naming it in The Art of the Impossible:
There's a short description from VH:
"An image of a ship, the eagle on its underbelly freshly painted, formed on the screen, and Saavik straightened in alarm. This ship was perhaps twenty percent bigger than the old warbirds, with more graceful lines than the K'tinga-class Klingon vessels that the Empire had used in recent decades."
This book was written in 1999, four years before The Lost Era Series started coming out. Adding more intrigue is that the warbird on the cover of the novel was a reuse of the D'Deridex seen on TNG and DS9. So, with a little extrapoliation, we can assume that the Amarcan is 20% bigger than the Ivarix, but smaller than the D'Deridex with a double hull. Maybe it's kind of like the Melak from New Worlds.
Klingon Vakk-class cruiser from The Art of the Impossible:
This ship was the first new class of Klingon cruiser since the turn of the century built after the attack on Narendra III. It's probably a step in between OP's Kleev and TNG's Vor'cha.
Cardassian scout from Well of Souls:
Nothing on this one. Probably looks like the Hideki-class from DS9.
Vulcan warp-shuttle T'Pol from Well of Souls:
Again, very little. The term shuttle is a misnomer as its big enough to have crew quarters and its own shuttlepod. Probably the evolutionary descendant of the warp shuttle from The Motion Picture.