I use Flight Simulator X, and Flight Simulator 2004 (FS9) religiously. Both can be had for relatively cheap, and through places like
http://www.flightsim.com , addons to enhance the realism can be found for free. If you have a newer computer with a nice graphics card I'd go with FSX. If you have an older computer with a stock video card, FS9 is a great option.
Also, there are many quality payware products for these programs. QualityWings Simulations has several. I have their 757 and love it dearly, and this year they released the long awaited 787 which appears to have been warmly received.
I installed X-plane 10 and hated it, but it it's probably just a personal preference.