Far be it from me to tell folks what to make, but I have to admit I've stopped downloading the modern age tanks and mech infantry units. I would go for a new M-60 and a T-72 for a couple cold war tanks, but other than that, I can't think of any place to put new tanks.
IMO, the area that needs the most attention is middle eastern units. Currently, I use the Immortal as a Holy Warrior in the Middle Ages, Lab Monkey's Eastern Pikeman, and the Ansar Warrior, but that's all there is.
If you ask me, here's what I'd want:
Ancient European Spearman(Germanic, not Greek or Roman)
Muslim Musketman/Rifleman(Maybe a mounted one too)
Napoleonic, Saber-wielding Cavalry
Greco-Roman Archer
Modern Middle Eastern Infantry
Some more...
European Middle Ages, pre-caravel sailing ship
WW2 Cruiser
Modern Destroyer
Early Knight
Apache Chopper(Maybe my most-wanted)
From my observations, any of those guys ought to meet wide acclaim.