What Magnum said, bang on sir! Don't forget the latest Steel Panzers mod w/ all the trimmings. My current favourite sim. The only thing missing for me is a desert Afrika Korps campaign. Also agree that ArmA 2 w/ Invasion '44 mod is just as excellent too; I get my Fallshirmjager fix there. Youtube gameplay videos are your friend

I just wanted to add a wildcard suggestion to the usual suspects... I'm currently playing a certain WWII game right now... and I'm stunned at how utterly brilliant it still plays after all these years:
Hidden & Dangerous 2 (with Sabre Squadron expansion). Probably, the greatest WWII tactical sim ever made? If you haven't ever played it, trust me, you must. It's like a potent mixture of Sniper Elite, Death to Spies, Hitman and oldskool Rainbow Six (when PC games used to be great). The thing I love about it is in the SP Campaign, the designers made various ways of completing the missions. You're free to do them as you see fit. Even the musical soundtrack is akin to an old classic war film score by Gerry Goldsmith or Ron Goodwin. I was also happily surprised it plays perfectly in Windows 7 x64.
Mission 1 Spolier...
Currently finishing up the first arctic mission in the SP campaign... and what a mission it is! Parachuted in with my team undercover of darkness.. a light snow is falling... met the Norwegian contact, approached the base, cut the fence w/ wirecutters... took out the guard dog (no choice, unfortunately)... retreated to the woods to take out the guards w/ sniper + sten + bren gun... inserted back via additional wirecut hole... infiltrated the underground base... took photographs of prototype Me262 intel... stole a German mountain/artcic uniform (including one of those nice "Steiner" M43 field caps)... went on a "Hitman" stealth-style killing spree w/ my Fairbairn-Sykes... blew up the base w/ timed explosives... split team into two groups, sniper and MG42 guarding the remains of the base, bren gun guy and me back to rendezvous w/ our contact and rescue the Spitfire pilot... picked up scoped K98 from dead German sniper and slaughtered the rest of the enemies patrolling the woods. While all this is going on, a truckload of stormtroopers has just turned up at the base so I switch to my MG42 guy and then my sniper in the tower to mop up the rest. Things got a little too hot for the MG42 guy so I retreated him to the tower and now both guys are up there, MG42 now switched to Sten gun, which works wonders on one of the stormtroopers (stupidly) scaling the ladder up to the tower, although I could've just as easily dropped a captured stick grenade on his head. Currently escorting the pilot (gave him a German helmet and K98 to boost the party) back to the base and the docks and hopefully no more nasty surprises (but I love those surprises, the game was designed beautifully). I have to say, this first mission has a definite "Where Eagles Dare" vibe about it. The tension is palpable.. so atmospheric, I can't rate it highly enough. 11/10!