If you're looking for combat flight sims, here's some I can recommend:
Combat Flight Sim 3 - WW2 - (I really like this game, the 'Firepower' addon improves the game a lot and allows you to drop nukes from the amazing Superfortress! The graphics are solid, the interface is nice, there's plenty of things to do and although the campaign lacks drama and a bit of atmosphere, it's a very competent and realistic sim). Not as many mods for this game as others although you can download small things like custom planes, particle FX, hud and cockpit fixes and ground objects, etc.
IL-2 Sturmovik - WW2 - (in many peoples' eyes, the very best combat flight sim ever, includes lots of mods and improved content, has a very avid community). Probably 'better' than Combat Flight Sim 3 as it has a very active community that Combat Flight Sim 3 lacks, although I don't think it's quite as strong graphically and if IL-2 is being looked at in its 'vanilla' form, I'd prefer to play Combat Flight Sim 3.
European Air War - WW2 - a good game although it is pretty dated and very hard to get running on modern hardware (I had to download a load of stuff on a lot of different forums to get it running).
Falcon 4.0 - modern - (some of the custom mods and other spin-offs (e.g. BMS) that have been made are amazing and constantly updated - check the wikipedia page). 'The Falcon 4.0 series is one of the longest running game series using the same code base in PC history spanning well over a decade.' The amount of content is crazy. There's a free version called 'Free Falcon' but I'd probably check out the advantages/disadvantages of each game/mod before installing.
F-22 Lightning 3 - modern - a nice sim focused around the F-22 fighter jet - more limited than the other games, lacks a real community and is more focused on just getting you to complete missions but I still have fond memories of playing it and it certainly has an atmosphere to it.
For normal flight:
The Microsoft flight sims are good, well supported and recommended by all. 2004 and X are solid and you might want to try the fairly new and free 'Flight' game (far more limited but really good looking). You can download a lot of custom terrain textures that are completely accurate using satellite data for 2004 and X (possibly other games too depending on which terrain packs you buy) which is really cool.
X-plane, never played it but, along with the Microsoft flight sims, it's the most 'complete' and realistic flight sim out there.
Just Flight has a lot of cool, addons, games, etc. just look at the amount of content here:
http://www.justflight.com/category/flight-simulators
There are soooo many flight sims out there although the best often have a great community behind them that keep things up-to-date and add custom content. That is an extremely important part of flight simulation imo.