Real Flight has the best record for value added. And they just went themselves one better. Or actually, 5 better.

G4 would not originally work with any of the AddOns that were made for G3/3.5. They had produced 5 of those AddOns and had shifted to producing Expansion Packs. Expansion Packs and AddOns were basically the same thing, lots of new airplanes, choppers, and flying fields, but they chose to call them by different names. Bottom line was they offered a bunch of additions to the original base programs. But you couldn't use the addons with the new version G4, although you could use the Ex-Packs. Real Flight promised from the first that they were working on G4 to get it to accept those AddOns.

Turns out they've just started offering newly modified old AddOns. They're taking each old AddOn content and coding it to work with G4. And you can download each for FREE ! If you had bought G4 and were ticked that you couldn't use your old AddOns, well, you now can simply download them for free. And if you were planning to buy G4 it will now have available a BUNCH of free addon stuff. 5 addons whether you had bought any before or not.

So if you're interested in a sim that is actively expanded periodically by the producer, and offers a pile of FREE expansion stuff, look at Real Flight's track record. Software companies that support like they support really are out of the ordinary.

BTW, they have a website that has FREE user-created models that work on G3/3.5 and on G4.