With the WW1 fighters, I want to recreate all the important fighters from the arms race that occured. New fighters were developed constantly, and a technology advanced at such a rate that a new type would be obsolete wihin a few months.
The order of appearance of some of the major planes (subject to change!):
1914
Morane Salnier L (Fr) - 1st ever plane intended to shoot machine guns
Pfalz A.lb (De)
RAF FE.6 (GB)
1915
Fokker E.III (De) - Fokker Scourge
Nieuport 11 (Fr, GB)
RAF B.E.2 (GB)
Airco De Havilland D.H.2 (GB)
RAF FR-2d (GB)
Vickers F.B.5 (GB)
Morane Salnier N (Fr)
1916
RAF FE.8 (GB)
Sopwith 1 1/2 Strutter (GB)
Sopwith Pup (GB)
Sopwith Triplane (GB)
Nieuport 17 (Fr)
Albatros D.III (De) - Bloody April
Spad S.VII (Fr, GB, US)
Fokker D.IV (De)
1917
Bristol F.2b (GB)
RAF S.E.5a (GB)
Sopwith Camel (GB)
Nieuport 24 (Fr)
Nieuport 27 (Fr)
Nieuport 28 (Fr, US)
Spad XIII (Fr, GB, US)
Fokker Dr.I (De)
Pfalz D.III (De)
1918
Fokker D.VII (De)
Sopwith Snipe (GB)
Junkers D.1 (De)
Some nice links on this subject:
Century-of-Flight.net - World War 1 Aerial Combat[url-http://www.wwiaviation.com/toc.html]WWIAviation.com[/url]