Have to agree with what Jim has said-lots of nice suggestions, but some things are way to specialized. I can think of hundreds of figures subjects that I would like, but sadly they arent going to make any money from producing figures that just a couple of people want. Polish figures for example are a nice idea, but for the mainstream of the hobby i cant imagine many people model Polish stuff, and I'm sure that the German fans would only want some captured Poles. I think its good to produce figures, for which there are a matching number of vehicles:
M1A1/ M2 crew in the armored vehicle crew body armor
1970's IDF centurion crew
1970's IDF infantry
Modern IDF infantry
Modern US special forces Humvee crew(seated)
Modern special forces in action
Modern US truck crews
Delta force ala 1993 Mogasdishu
US Rangers " "
Modern US infantry figures from around the initial Iraq invasion(Thunder run!)
Modern Brits in A stan and Iraq
Modern Canadian infantry/AFV crews would appeal to a lot of people
I think Vietnam has been done to death by Dragon, Verlinden, Hobby Fan and a few other companies so I wouldnt bother going there. Except perhaps a Pibber crew, or some wounded GI's.
British ww2 recieving medical attention
British WW2 truck drivers
British tank riders
Desert rats in dynamic poses-we got basic infantry, hows about guys cutting wire, mine clearance, bofers crew, wounded, digging in, mechanics etc
captured Afrika Corps and Desert rats
101st Airborne BOB, holding the line at Bastogne etc
Captured Americans
Captured french
Captured Russians
Wounded Russians

Those are just a few ideas I could come up with of figures that would fit right in with many of the vehicle releases on the market today. I think you need to decide who you wish to appeal to: Figure modelers, armor models or diorama guys. You will find that each of those groups have different interests, figure modelers seem to like less dynamic poses, I would class some of Alpines stuff as appealing more to just figure painters. Whereas the diorama builders/ armor modelers I imagine will want figures that can be used to convey a story or a scene. I might be wrong but I believe most of what I have listed about would be good subjects that would sell. Obviously there is some bias toward modern stuff, but ive tried to list stuff that isnt already available and based on the interest ive seen of these vehicles would sell. Also modern reference is damn easy to come by. But anyway, i wish the best of luck to these guys and hope they come up with some cool releases!

Its a shame that there isn't enough resin sculptors out there that cannot create a company who specifically make figures to order for the modeller .At a price.

I like all ideas of what everyone has mentioned so far with the large number of suggestions catering for a wide variety of figures.

Good luck to the people who will try and get some form of idea of what to do with what's been suggested in this thread.

1° I'll second Hisam comment : when you look at war pictures you see that soldiers were wearing clothes not a very "conventional way" : pants are large and got holes at the knees, shirts are open, helmet is worn on the side of the head and not on top, shoes are not laced. I'm a bit disappointed because figures company (mainly plastic ones) present soldiers as if they were on parade : they are all dressed the same, in a "clean" way.

2° Another comment stated that people in real life are not all the same size, some are tall, some small, some fat, some got big muscles, some have mustache, some have long hair (mainy late war pictures of german show very long hear, unlike what the common people think).

I'll second also Jim comment : Jim Saunders headsets are just marvelous. But there is no other company which produces good headt sets. Let's take a good example : many of the comments asks for common wealth troops. Release a set of Gurkhas hat, scotish beret, french képi, take figure from dragon/minia/masterbox, some scratch and with some work you've got your commonwealth figure.