For freeware the choice is nowadays extremely wide. Also, a little part of those freeware planes are ex-paywares, mainly the IRIS birds mentionned by other members earlier.
From what you wrote you are mainly looking for military-style planes, so I'll skip the civilian ones.
I'll also skip the FS9 port-overs since you will probably already know most of them. I'll talk only about the FSX-native format planes.
In general freeware, I would recommend you the various birds created by Tim Conrad, some of them already exist in earlier versions for FS9, the FSX versions are new models of the same birds, compiled in FSX native format with better textures, VCs and more detailled shapes.
There are also quite a lot of classic old military planes available at Britsim.com, classic jets like the Vampire, Venom, Hunters and more.
You might want to take a look at the birds created by the French team Restauravia, mainly the Dassault Mystere, which has some great visuals, an excellent virtual cockpit, great sounds and fantastic flight model ! Same for their Epislon jet. For French stuff, I would also recommend you to download the Etendard from the Royale French Navy website, which is on the same level of quality of the other birds mentionned before.
Oh, and
of course the Tomcat and T-45 created by Dino Cattaneo

The last freeware classic jets that comes to my mind are amongst the best ones:
- the F-104 StarFighter created by SimSkunkWorks. It's FSX-native, it has a beautifull external model, a very good virtual cockpit, great sounds and an excellent and extremely challenging flight model !
- the Mig-21MF which is almost on the same level than the F-104, but I can never remember the exact author name

For payware I would recommend three things:
- for modern military, the VRS F-18 Super Hornet, it's simply the greatest modern military bird available so far in terms of realism, visual details, virtual cockpit complexity and interactivity in the cockpit.
- for classic warbirds, the P-47, the B-17 and especially the Spitfire made by A2A
with the Accusim extention !! Nothing, absolutely nothing will come close to that. Just take a look at the official presentation videos of those birds on the site:
- there wil be an Accusim Mustang by A2A in the near future, but in the meanwhile you might want to take a CLOSE LOOK to the WarBirdSim Mustang, which is without any doubts one of the most beautifull 3D model ever created in the history of Flight Simulator.
Here are the videos showing what "Accusim" means.
[media width=640]http://www.youtube.com/watch?v=_P-7e3RN5_Q&feature=player_embedded#![/media]
[media width=640]http://www.youtube.com/watch?v=nsPjn1L0elw[/media]