Pretty much got them all (you could probably have worked that one out from my forum name I guess), but the one I mess about with the most is probably Condor The Competition Soaring Simulator, as it has a flight model which blows every other PC-based flight simulator out of the water and is certainly the only one that you can spin properly in; in fact, the reason I decided to buy it was when I saw a demo video of one of the gliders spinning, and thought 'Yup, that's exactly what it's like in real life!'. Plus it runs great even on a moderate PC and it has a great online community as well as a competition league for tasks and races. Great with Track-IR too. And handy when it's too rainy to go and fly the real thing!
I like the flight model in IL-2, but the single-player game itself is a little lacklustre and the AI is somewhat questionable, although it does come into its own online against human players.
FSX is another favourite, but the flight modelling is not brilliant, however it is great for variety, modding possibilities and the modelling of complex systems, although many of the better aircraft are only to be found in FS9, so I use that too for things like the PMDG Boeing 747.
I occasionally wheel out some of the older ones like B17 and Gunship, and the free WW1 add-on 'Over Flanders Fields' is great for CFS3, so that gets a showing every once in a while.
Not forgetting Falcon Allied Force of course, which definitely has the best dynamic campaign of any flight sim, and is also a blast online. another one that's great with Track-IR and it runs good on a moderate PC too.
So, yup, I do use quite a lot of them :rotfl:
Couple of pics from Condor below, one is a Ventus 2 coming up on 18,000 feet over Mont Blanc, the other is an ASW 28 on aerotow at the start of an online race.

Chock