There has been a discussion on the HO page recently about smaller locomotives (this is in a scale dominated by Class 1 fans of big engines, including myself). However, there was also a discussion of some narrow gauge and industrial material, which included these links here. Perhaps you can find interest and inspiration here:
We start off with a master link, Northeast Railfan (which also has a number of photo rosters, including B&O and CNJ we've been using elsewhere):
http://www.northeast.railfan.net/industrial.html
This is just some of what is here:
http://www.northeast.railfan.net/diesel100.htm
http://www.northeast.railfan.net/diesel112.html
http://www.rr-fallenflags.org/porter/porter-ind.html
http://www.over-land.com/rrporter.html
Six pages on Plymouth Locomotives, from Plymouth, Ohio; item of note, most were shipped via the B&O, suggesting some interesting flat car loads. Most photos on this site can be enlarged by clicking on them:
http://www.northeast.railfan.net/diesel81.html
http://www.northeast.railfan.net/images/plw1987.jpg
Look who owned this one!
http://www.northeast.railfan.net/images/tr_bo25.jpg
Another interesting owner, and check out the exhaust stacks:
http://www.northeast.railfan.net/images/pe1646.jpg
Amherst Barge in West Virginia:
http://www.northeast.railfan.net/images/ahs0.jpg
This one is the prototype for a Mantua/Tyco model from the early 1960s:
http://www.northeast.railfan.net/images/lbr3.jpg
It's supposed to be a different locomotive from the link above, but I'm not so sure. In any event, it's the same type, on the standard-gauge section of the East Broad top Railroad and Coal Company; photo locations are at Mt. Union, Pa.:
http://www.northeast.railfan.net/images/lbr3a.jpg
http://www.northeast.railfan.net/images/lbr3b.jpg
For plow, work, and towing service on transit lines, Boston and San Francisco, the latter on 5' 3" gauge:
http://www.northeast.railfan.net/images/mbta04443.jpg
http://www.northeast.railfan.net/images/bart0.jpg
A burly 100 tonner on narrow gauge, for Bethlehem Steel:
http://www.northeast.railfan.net/images/bscx30.jpg
I believe Model Railroad once published drawings for this one:
http://www.northeast.railfan.net/images/ils49.jpg
http://www.rrpicturearchives.net/showPicture.aspx?id=1914456
http://www.northeast.railfan.net/images/tr_moy58.jpg
http://www.northeast.railfan.net/images/cc106-6.jpg
Westinghouse page:
http://www.northeast.railfan.net/diesel109.html
This Westinghouse unit is preserved and reported operational at the Pennsylvania Trolley Museum in Washington, Pa.--a museum I can personally recommend:
http://www.northeast.railfan.net/images/tr_arm_b73.jpg
http://www.northeast.railfan.net/images/arm_b73a.jpg
http://www.railpictures.net/viewphoto.php?id=254284
A sister unit, No. 71, which, judging from the background, is also preserved:
http://www.northeast.railfan.net/images/ascB71.jpg
The photo says this is on the Northampton & Bath, but I'm not sure; she looks more like something from eastern Europe than North America, and what steam locomotive is that behind the diesel?
http://www.northeast.railfan.net/images/tr_nb1601.jpg
Can't ignore industrial steam:
http://www.northeast.railfan.net/industrial_steam.html
Proper locomotives are painted black and burn coal--except when they don't:
http://www.nrhs.com/web_exclusives/fireless_cooker/index.html
http://www.northeast.railfan.net/steam21.html
It's surprising how common some of these Porter "fireless cookers" once were, and late in era, too; some have been running in recent years. And take note, in the first photo, of the big 0-8-0 Heisler job in the background; it's still around, in the Railroad Museum of Pennsylvania:
http://www.northeast.railfan.net/images/ppl4093a.jpg
Same engine some years later--"Take that, Thomas!":
http://www.railpictures.net/viewphoto.php?id=244912
Another shot of the Heisler 0-8-0:
http://www.northeast.railfan.net/images/tr_ppl4094.jpg
One of two common later designs from Porter:
http://www.rr-fallenflags.org/misc-u/ues-s4ags.jpg
http://www.rr-fallenflags.org/porter/page48h.jpg
The other was an 0-6-0; reportedly one of these engines was still in use at a power plant in Pennsylvania at least into the 1980s, and was rigged up for remote control, like some diesels in steel plants:
http://www.rr-fallenflags.org/misc-p/pplc-sunk-bv.jpg
C&O had three of these 0-6-0Fs, for use in the literally explosive atmosphere of the chemical plants in Charleston, W.Va. The were replaced with diesels, which had to use a "handle" of up to six idler flats to reach into some of the areas these steamers could go with safety. The photo location is at the yard and locomotive facility in South Charleston; the wooden trestle in the background is the southern approach to a bridge over the Kanawha River that lead to an interchange with the B&O (former Coal & Coke) and New York Central (former Kanawha & Michigan) lines on the north bank. This bridge was also shared with the local trolley system until that service dried up in the late 1930s.
http://www.rr-fallenflags.org/co/co-s35qlr.jpg
This site is so useful, I'm posting it here. Most of it is class 1 and diesel, but there is much else, too. Mr. Elwood deserves great credit for sharing so many photos.
http://www.rr-fallenflags.org/#c
Some more Plymouths:
http://www.google.com/images?hl=en&resnum=0&q=plymouth+locomotive+photos&um=1&ie=UTF-8&source=univ&ei=H0bRS4CNO4rq9QT3rOWzDw&sa=X&oi=image_result_group&ct=title&resnum=1&ved=0CA8QsAQwAA
http://www.ironminers.com/mineforum/viewtopic.php?p=11587&sid=0404daa453bd333ec89fcefcb7a14e14
Industrial heritage:
http://www.ironminers.com/
http://www.undergroundminers.com/
Enjoy.