Introduced: circa 1980 (generic 4-6-0 and 4-4-0), 1999 (Illinois Central "Casey Jones" 4-6-0) and 2011 (4-6-0 Camelback)
I have never actually owned any of these models. Further, what I "think" I know about them has been pieced together from a little bit of actual fact and a whole lot of deduction (IE, before we proceed any further, go find your proverbial grain of salt).
Anyway, it's my understanding that there was (once upon a time), a German outfit called "Intermodel" that (circa 1980) released the above two "generic" American 4-4-0 and 4-6-0 steamers. The above pictures are actually scans from a 1980 Intermodel catalog that were sent to me by a fellow N scaler in Germany. The catalog description for the 4-6-0 states "American steam locomotive with separate tender and spark arrester", whereas the description for the 4-4-0 simply reads "American steam locomotive with separate tender".
Somewhere during the tangled course of post-1980 human events, Intermodel changed their name to Westmodel. Further, an American company by the name of Aspenmodel became their importer. Circa 1999 they started offering up the above-pictured Illinois Central "Casey Jones" 4-6-0 on their website, and in 2011 added the above-pictured Camelback 4-6-0 to their roster. All four of these models consist of custom brass shells designed to be mounted atop a standard Fleischmann steam locomotive mechanism (#7161). In the case of the 4-4-0, the forward set of drivers has simply been removed.
I don't know much about the original 4-6-0 and 4-4-0 releases, but according to the Aspenmodel website the "Casey Jones" 4-6-0 is available either ready-to-run or as an ala-carte shell-only kit. And as of this writing (2008), the RTR steamer is all yours for a mere $700. As for the Camelback, that one is only available as a kit (and sans mechanism). The price is $390 (as of 2011). There is no indication on Aspenmodel's website as far as what prototype the Camelback model might be based on, but others have speculated that it appears to be a replica of a 1912 Central of New Jersey L7 (built by Baldwin Locomotive Works). Said L7 was very similar to CNJ's L6a (1910), L7a (1913-1914), and L8 (1918) Camelback locomotives, all of which were re-designated as the T-38 Class in 1945.
As noted above, I have never owned any of these Intermodel/Westmodel locos. However, the Fleischmann 7161 steamer is readily available, so let's talk about that instead -
The motor and driving wheels all live inside the tender, whereas all pickup is derived from the six drivers on the locomotive (transferred back to the tender via wires). Four of the eight driving wheels on the tender come equipped with traction tires. The motor is a fairly large 3-pole / straight-wound affair that does a pretty good job of moving the thing around. Unfortunately, throttle response is pretty coarse - it starts off fast and quickly accelerates up to warp factor nine by the time you get into the meaty end of the throttle. Given the relatively small pick-up footprint (not to mention the primitive wheel wipers on the drivers), stalls and overall jittery behavior are a big problem. I've also run into problems with the worm not meshing properly with the worm gear (the end result being a lot of noise). Also, the metal drawbar seems prone to causing the occasional short-circuit. So, kind of interesting, but ultimately not a very impressive locomotive.
As far as the 4-4-0 goes, I have no idea what affect the removal of the forward drivers might have had on this mechanism (having never even seen one so configured), but it's not a huge leap to suppose that removing a third of the pickup footprint didn't help out the cause...
Trivia - back in 1972, an American company called "Rocky Mountain Models" released a remarkably similar 4-6-0 using the same Fleischmann mechanism. I'm told that that shell was also manufactured by Intermodel (although at this point in history it seems to have vanished from the universe).
Update - as of this 2016 writing, rslaserkits (USA) has also signed on as a re-seller of Aspenmodel locomotives and rolling stock.
Grade: C (for the Fleischmann 7161 mechanism)