A fact corresponding with the huge historical importance of the Great War are the fairly high number of museums - especially in Europe - more or less dedicated to WW1. Here are mentioned some of the most important ones.
The Royal Museum of the Army and Military History in Brussels, Belgium.
This BIG museum is located in one of the buildings of the Cinquantenaire Park in Brussels and contains about one hundred thousand items. This collection makes it into the top military museums in the world. The WW1 collection is remarkable, containing both tanks (one Mk IV, one Whippet and one FT-17) numerous WW1 guns (could it be around 50?) and a huge amount of weapons, uniforms etc. Albeit traditional in presentation, the collection itself is just astounding.
Check this link: http://www.klm-mra.be/ Or this one: http://www.planetware.com/brussels/belgian-army-museum-and-museum-of-military-history-b-br-arm.htm
The Army Museum in Paris
Another BIG museum, with a really impressive collection. The WW1 Section has recently been redone, and it's very nice: austere, informative. There is no clutter and no surfeit of things, but if you are interested in just the hardware, you could be just a tad disappointed. Well worth a visit though! Highlights: A FT-17 Cannon, a "75", two different creep-tanks, plus a number of rare French mortars.
Check this link: http://www.invalides.org/pages/anglais/infos_a.html
The Imperial War Museum in London
One of the best. It has an incomparable collection covering all aspects of twentieth and twenty-first century conflict involving Britain and the Commonwealth. Very nice WW1-collection, plus a "Trench Experience" - if you like that kind of thing. Among the highlights: a Mk V, plus some WW1 heavy guns, and some ordinary field guns. Very well kept items. Of course best on things British.
Check this link: http://london.iwm.org.uk/server.php?show=nav.00b (Web users can now access over 6,000 highlights from the collection, including photographs, works of art, audio extracts, aircraft and vehicles, documents and library material as well as detailed catalogue information on over 160,000 items.)
Museo Storico Italiano della Guerra in Rovereto, Italy
The Italian War Museum was founded in 1921 in remembrance of the First World War and in it are preserved arms and documents relating to wars from the 16th to the 20th centuries. As well as its permanent collection, it organises temporary exhibitions, and publishes books and articles dealing with WWI and other 20th Century conflicts. Perhaps the best, beside the Military Museum in Brussels. A very big collection of uniforms, weapons and equipment plus a big number of WW1 Artillery pieces, some rare. Highlights: One of the worlds only two surviving Austro-Hungarian 30.5cm M.11 "Schlanke Emma" is kept here. Of course best on Italian and Austro-Hungarian topics. Beautifully situated in an old castle at the foot of the Alps. Perhaps a bit of the beaten track, but it is worth the effort!
Check this link: http://www.museodellaguerra.it/eng/index_eng.html
Musée des Blindés in Saumur, France
This is not only the worlds biggest and most well-stocked AFV museum, it also prides itself in having many of its exhibits in perfect working order, including some tanks almost 90 years old! The WW1 department is not big - it lies just at the entrance - but, ah, the contents! The worlds only surviving S:t Chamond and Schneider C.A.1 can be seen here, beautifully restored - the Schneider is actually a runner - with complete interiors. Amazing. In additions to this there is some other WW1 exhibits, including a running FT-17, a FT TFS waiting for restoration and a Renault Truck. Also, tucked away in the other departments are some objects with WW1 interest, like a WW1-type forage wagon, the only one surviving in Europe.