This list was compiled and kindly provided by noted blogger Matt Golding  for the benefit of those determined to acquire a 19th century army or two.   Non web based companies have not been included.
(last updated:   23 April 2018)

Askari Miniatures  (25mm)
Intended as French colonial figures there are a number of models suitable for the Crimea, Risorgimento, and Franco Prussian Wars.

Aude Miniatures  (15-20mm)
Interesting range of predominantly 1848 Risorgimento figures (plus Garibaldini in 20mm).

B and B Miniatures  (20mm)
Chunky 20mm figures covering the Franco Prussian War.

Baccus  (6mm)
Growing range of 19th Century figures, including the Risorgimento and Franco Prussian War suitable for the Austro-Prussian War.

Baker Company  (25mm)
Carries the 1866 range of Austrians and Prussian started by Helion in the 1990s.

Battle Honors  (25mm)
1859/1866 French, Austrian and Saxon figures. Compatible in size and style with Wargames Foundry.

Castaway Arts  (25mm)
Franco Prussian War figures from Australia. Compatible in size and style with Wargames Foundry (slightly slimmer).

Eagle Miniatures  (15mm)
Franco Prussian War figures.

Essex Miniatures  (15mm)
Franco Prussian War figures.

Eureka  (15/18mm – 25mm)
Crimean war and other smaller ranges in 15/18mm Small, infantry only, 1864 range for Second Schleswig Holstein War.

FreiKorps 15s  (15mm)
Extensive coverage of 19th Century conflicts in 15mm.   If you cannot find it anywhere else then it will probably be in their catalogue.

Grenadier Productions  (15/18mm)
Not strictly European, but a large range of figures covering the Wars of Liberation in South America following the Napoleonic wars.

Heroics and Ros  (6mm)
The original 6mm figure range; wide range of figures including Napoleonic and Franco-Prussian War that can be used for the Austro-Prussian War and Risorgimento.   Not compatible with Baccus figures.

Outpost Wargame Services  (15mm)
Franco Prussian War figures.

Irregular Miniatures  (2-54mm)
Extensive range with figures suitable/adaptable to many European conflicts.   Also very useful for wagons, artillery etc.

Lancashire Games  (15mm)
Broad range of figures covering most European conflicts from the Crimea to the Balkans.

Legio Heroica  (20mm)
A small but expanding range of 1848 Austrian and Italian figures covering the First War of Unification.

Magister Militum  (10mm)
10mm Crimean and Franco Prussian war figures.

Minifigs  (15mm)
Crimean and Franco Prussian Wars ranges back in production again.

Mirliton  (15-25mm)
Covering the Italian Risorgimento.

Old Glory 15s  (15mm)
Suppliers of Old Glory 15s and Rank and File 19th Century European War ranges.

Pendraken  (10mm)
Highly regarded figures from the Crimea to the Franco Prussian War.

Perry Miniatures  (25mm)
Large First Carlist War range.

Tumbling Dice  (20mm)
Crimean War range, foot figures all wearing greatcoats only. Suitable for Inkerman etc.

Wargames Foundry  (25mm)
A large range of Crimean and Franco Prussian War figures.

Waterloo to Mons  (25mm)
A growing range covering the First Schleswig War.