The excellent Luftwaffe 1946 rules by Marty Fenelon. These are a set of WWII rules designed for mass combat; typical scenarios are 12-24 aircraft per side, suiting them admirably to play with 1/600 aircraft. The rules are hex based, and include air-to-air, air-to-ground and surface-to-air combat. They also include 10 scenarios, ranging from straight-forward historical encounters to the hypotheticals which give the rules their name.
It should be emphasised that in spite of the title, the Luftwaffe 1946 rules are admirably suited to historical WW2 games, being a refinement of the excellent Blue Skies series. The stats and scenarios enclosed cover a large number of aircraft from 1944 and 1945, and earlier periods are easily catered for.
Includes stats for 74 aircraft types, ranging from the P-51D Mustang to the propsed Arado 555-1 Amerika Bomber. In addition the Luftwaffe 1946 website (www.luftwaffe1946.com) will soon have a spreadsheet enabling you to produce stats for any aircraft based on its historical performance figures. In the meantime I'm happy to help with figures for any particular types you may want to field.
The rules weigh in at 80 pages plus a further 8 of card inserts (aircraft summaries and play sheets.) Don't be put off by the length, though; the basic combat mechanics are quick and easy; the page count includes those, advanced and optional rules for adding more detail where desired, background material, and scenarios.