Starlancer for me.

I still remember great story, and the best thing in the game was communication system between you and enemies. No better thing like to send a message "You're going down!" and receive the answer while after ;)

I always enjoyed the Wing Commander games, especially Privateer, which was my first GOG purchase, a few weeks ago. The Descent games were fun too, though those aren't really space sims, but the Freespace series...a friend copied the first one for me back in '98, and it was like love at first sight. Amazing atmosphere, very good controls, and a real sense of scale. Freespace 2 was even better. I still have a retail copy of it, but it's too damaged to use, sadly.

Rebel Assault games are not space simulations, part of the games is but the rest is not, if I remember correctly

TIE-Fighter no contest
Of course, X-Wing with the Death Star run comes very close.

Kind of nitpicky, don't you think? The craft you pilot in those games are all space worthy, and use the same controls. Seems more fair to clump them in with space simulation games than with normal flight sims.

I would recommend just going ahead and playing it when you get the chance even if you don't have a joystick as I don't think the game really needs one as much as some other space sims that have been mentioned.

The combat in X3 isn't fast paced or difficult enough to make having a joystick a necessity. I only found it useful early on when flying around in a smaller fighter and even then the mouse and keyboard is usually good enough, especially in X3: Terran Conflict which has better mouse flight than Reunion.
I actually have a joystick but I don't use it much for X3 unless I have it already plugged in from playing another game.

So not EXACTLY a space sim...but Descent 1&2 are the best games ever in my opinion...and if you like space sims and or FPS's you'll most likely enjoy it.

I'd definitely suggest getting Rebirth (http://www.dxx-rebirth.com/) For them...they're here on GOG

If I remember well, when it comes to flying ships, you either control the turret or the direction of the ship. And in that latter, you only have limited possibilities as to the direction to take (ex : RA II and the tie fighter in the canyon)

I was not saying it is a flight sim and not a space sim. I was saying it is not really either. It is a mix a different gameplays. A nice mix, but not a flight/space sim to me
Rogue Squadrons are flight sim, to me, for instance

If you want to have fun at some point in time, do yourself a favour and install the German version of Starlancer. Though you might not actually understand the language, it is just great to hear how awful the German language with a terrible American accent can be. A complete and miserable failure... xD

Ah, it's been long enough since I played, that now I can't remember. I thought that there was more flying involved than that.

This.

Terminal Velocity was awesome. Not really a "space" sim per se, but man was it fun. I guess this topic is heading in an "awesome joystick games" direction.

Space Sims. My favourite type of game :) I see lots of great sims mentioned so far but for me the Elite series will always be the best. Thankfully there are open source remakes of all 3 games.

For Elite there is Oolite. Elite the way it was always meant to be, here is a link http://www.oolite.org/download.shtml
Also dont forget the oxp add ons (Oolite Expansion Packs) too here [url=http://wiki.alioth.net/index.php/Category:Oolite_expansion_packs]http://wiki.alioth.net/index.php/Category:Oolite_expansion_packs[/url]
Gameplay vid here http://www.youtube.com/watch?v=mf0R3C-kPOo

For Frontier Elite 2, there is Pioneer (work is still under way on this project with monthly updates, but there is a playable alpha to be found here) http://pioneerspacesim.net/download
Incidentally, the dev team are always looking for ideas or people to contribute work (models, missions ect) to put into the game. If you drop by Space Sim Central, have a look through the threads. here is a link http://www.spacesimcentral.com/forum/index.php
Gameplay vid here (note this was a very early alpha) http://www.youtube.com/watch?v=1aVf-8qVdsg

Finally First Encounters Elite 3 had a graphical make over by some Russian devs called FFE3D. Here is a link to that http://spacesimcentral.com/downloads/ft2.php?dir=/FFED3D
Gameplay vid here http://www.youtube.com/watch?v=p7ip5orUlDM

Have fun people! ;)

Rebel Assault I/2 were essentially FMV games - I only played Rebel Assault 2 and it was a lot of fun.