IL2: 1946 The only good one I can think of. trust me, Microsof Combat Flight Simulator (at least, imo) is rubbish compared to it. the only downside, it doesnt have internet multiplayer.
its almost the same game as IL2: Forgotten Battles + Ace Expansion Pack + Pacific Fighters + PE addon, IL2 1946 is just in 1 box (with some extra contend), if you really have to have multiplayer over the internet tough, you'd need IL2:FB + AEP + PF to do so (wich would most likely cost more )
Edit: arg, nvm, you're looking for a modern one. (I take that as you want modern aircraft?) I still find Lock On and Falcon 4.0 Allied Force to be the best ones there still.
I'm actually looking for new ones myself tough, since I've played those a lot already.