Campaigning with the Duke of Wellington & Featherstone. Solid scholarship on the battles of the Duke of Wellington is combined with a light-hearted look at visiting the fields and gaming the battles of the Peninsular War. Includes a set of rules written by the great Featherstone himself.
Armati is a fun, fast playable set of rules.
Warmaster Ancients is an innovative set of rules that has now morphed into Black Powder, et.al.
Playable Napoleonic Wargames is a tactical set that focuses on the Peninsular War and includes a campaign system and map.
German Tanks of World War II is a great reference book with many pictures I have not seen elsewhere.
Space: 1889. The original Steam punk rules that allow you to live in the world of H.G. Wells, Jules Verne and others.
Space: 1889 Soldier's Companion. The Miniature war game rules for 1889. Great also for historical gaming.
Space: 1889 Conklin's Atlas of the Worlds. Every traveler needs a map!