How about a model of this big guy?

http://www.gearedsteam.com/shay/images/yosemite_mtn_n_sugar_pine_rwy_10.jpg

Here is another good idea.

http://www.gearedsteam.com/climax/images/wild_goose_rr_2012.jpg

Strange, isn't it? 

Here is a good example of a class A.

http://www.gearedsteam.com/climax/images/rigbee_&_hugh.jpg

Maybe this site will help.

http://www.phoenixsound.com/library/other.html

Here are some steam locomotives of the WHite Pass and Yukon Route.

http://www.steamlocomotive.info/vlocomotive.cfm?Display=780

http://www.steamlocomotive.info/vlocomotive.cfm?Display=1973

http://www.steamlocomotive.info/vlocomotive.cfm?Display=1150

http://www.steamlocomotive.info/vlocomotive.cfm?Display=1757

http://www.steamlocomotive.info/vlocomotive.cfm?Display=4

http://www.steamlocomotive.info/vlocomotive.cfm?Display=5

Here is an idea for a bachmann set with rolling stock.

http://www.steamlocomotive.info/vlocomotive.cfm?Display=5872

The lumberjack steam train is not narrow gauge.  And I have a couple more ideas.

http://www.steamlocomotive.info/vlocomotive.cfm?Display=1523

http://www.steamlocomotive.info/vlocomotive.cfm?Display=244

And how about compressed air locomotives?

http://www.steamlocomotive.info/vlocomotive.cfm?Display=5452

Don't forget what I said about railcars/railbuses/doodlebugs.

Just out of curiosity, are there any narrow gauge steam dummys?

I've seen it before. They don't have much narrow gauge, though.

Here are some more bizzare geared engines. Enjoy!

http://www.gearedsteam.com/climax/images/rigbee_&_hugh.jpg

http://www.gearedsteam.com/climax/images/wild_goose_rr_2012.jpg

http://www.gearedsteam.com/heisler/images/amsler_n_campbell_2.jpg

http://www.gearedsteam.com/heisler/images/wh_eccles_lbr_3.jpg

http://www.gearedsteam.com/heisler/images/pacific_coast_borax_2.jpg

http://www.gearedsteam.com/heisler/images/wt_smith_lbr_11_3ft.jpg

http://www.gearedsteam.com/shay/images/shay_cn_5.jpg

http://www.gearedsteam.com/shay/images/cobbs_&_mitchell.jpg

http://www.gearedsteam.com/shay/images/good_roads_construction_co-3118.jpg

http://www.gearedsteam.com/shay/images/h_kalbach_lbr_4.jpg

http://www.gearedsteam.com/shay/images/mason_n_oceana_rr_2.jpg

http://www.gearedsteam.com/shay/images/yosemite_mtn_n_sugar_pine_rwy_10.jpg

Here are ideas from the east broad top

http://www.ebtrr.com/equip/diesel.html

http://www.ebtrr.com/equip/gas.html

And how about these cars...

http://www.cumbrestoltec.org/rs.php?num=Hinman

http://www.ebtrr.com/equip/passcars.html

http://www.ebtrr.com/equip/freightcars.html

I have noticed that bachmann is planning to make an open air coach in HO.
How about one in On30, too? 

Here are some more ideas. I've heard that Accucraft is making a model of an 0-6-6T.

http://www.ironhorse129.com/prototype/MasonBogie/american_fork_044t.htm

http://www.ironhorse129.com/prototype/MasonBogie/brplrr_244t.htm

http://www.ironhorse129.com/prototype/MasonBogie/CPS_0-6-4.htm

http://www.ironhorse129.com/prototype/MasonBogie/Dup_286t.htm

http://www.ironhorse129.com/prototype/MasonBogie/dspp_286t.htm

http://www.ironhorse129.com/prototype/MasonBogie/dspprr_266t.htm

http://www.ironhorse129.com/prototype/MasonBogie/mexico_266t.htm

http://www.ironhorse129.com/prototype/MasonBogie/NewBrunswick.htm

http://www.ironhorse129.com/prototype/MasonBogie/npcrr044.htm

http://www.ironhorse129.com/prototype/MasonBogie/npcrr066.htm

http://www.ironhorse129.com/prototype/MasonBogie/NS_Georgia_044T.htm

http://www.ironhorse129.com/prototype/MasonBogie/nymbrr_044t.htm

http://www.ironhorse129.com/prototype/MasonBogie/peach_bottom_066t.htm

http://www.ironhorse129.com/prototype/MasonBogie/RiverduLoup.htm

http://www.ironhorse129.com/prototype/MasonBogie/Stockton_044t.htm

Note: If these are too many ideas, please don't get mad at me. I'm just a train fan.