I have taken the time to give Jeff's earlier post some more thought (along with the comments received), and would like to offer the following suggestions, for what they're worth:
Off of the top of my head, my currently painted 25mm Ancient armies are:
Greek Hoplites - Corinth
Alexandrian Imperial - Corinth
Syracusan - Ophir, Koth, Corinthia
Carthaginian - Ophir, Koth
Feudal Scots - Nemedia
Feudal Spanish - Zingara
Samurai - Khitai
I know that I have unpainted lead for these 25mm armies:
Ancient Indian - Vendhya
Illyrian - Corinth?
Gauls - Hyperborean or Cimmerian
Early Imperial Romans - Argos
Ayyubid Egyptian - Iranistan
Knights (3/4 painted) - Aquilonia or Nemedia
In 15mm I have the following painted armies:
New Babylonians - Shem
Greek Hoplites (early & late) - Corinth
Late Imperial Romans - Argos
Franks/Goths - Hyperborean?
Arab Conquest - Iranistan or Turan, depending on makeup
Medieval German Kn - Aquilonia, Nemedia or Brythunia
This should give you some general ideas, and you can always add a few "specialty" or command figures that really make the army "fit" the profile. You could even combine troops from some armies to create a Kingdom. Check out some of the Hyborean links to the right if you haven't already Jeff.