PC flight simulators have proven very popular. The current generation of gaming PC's deliver performance that only a few years ago was the province of supercomputer labs. It's not surprising that aviation enthusiasts have written flight simulator software to take advantage of this computer power.
For airplane pilots, X-Plane and MS Flight Simulator X are excellent but they offer only limited glider features. Fortunately, sailplane pilots have a choice of excellent simulators written specifically for soaring. To satisfy purists, I have to say that no desktop computer will substitute for actual flying in real sailplane. Still, PC simulators have a much to offer.
As I write this a joystick sits to the right of the computer screen. It's always there ready for use. My application of choice is Condor, The Competition Soaring Simulator. (www.condorsoaring.com) I use it to simulate complex flight maneuvers. Condor has never failed to produce dead accurate flight dynamics. For the flight instructor, the greatest value Condor offers is as an "animated white board" used instead of drawing diagrams on paper or classroom white board. Animating a maneuver on a flight simulator has great training value.
I'd like to offer an observation about the way simulator pilots learn. All of the second to second situational information from the simulator comes to the pilot through the computer screen - in other words, through the eyes. To fly a PC simulator well and especially to land, you have to learn to see subtle visual clues. Really learning to see - to use your eyes efficiently - is hard work but visual skills are what make a superior aviator. I think this is why PC simulator enthusiasts do so well in real-world flight training. I've encountered youngsters with hundreds of hours on PC simulators whose flying skills were very impressive on their first flight in a real glider.
Many pilots have built "cockpits" with accurate panels and working controls. The outside view is projected on a large screen in front of the "cockpit". If this is over the top, at the very least get a good set of rudder pedals. Unfortunately, no commercially available rudder pedals really match glider pedals but you can easily build your own from plans available on Internet forums.
Condor contains a complete "flight school" that expertly demonstrates maneuvers, then allows the student to practice them. The school starts with basic skills and continuing all the way to competition flying.
Condor is largely Europe-centric with most of the photo-realistic scenery available for that part of the world. Still, flying a simulated glider through the Alps is really spectacular. You can make thermals visible with the "thermal helper" which purists consider 'cheating' but this help the uninitiated visualize how thermals are distributed in the sky.
Condor supports online multi-player contests. There are dozens of online contests you can participate in every week. You see the other players gliders and they see you. I know of several top contest pilots who spend winter evenings competing with other pilots around the world. If you try it, prepare to get beat - these people are GOOD and they'll leave you in the dust. If you don't let your ego get bruised, it's a great way to learn competition flying.
In addition to Condor, Sailors of the Sky (www.sailorsofthesky.com), SFS (www.sfspc.de) and Silent Wings (www.silentwings.no) are excellent choices. Silent Wings offers something special - you can download IGC flight logs from a contest and play them back simultaneously. You get to see the action from the cockpit of a real competitor. 50+ gliders in the same thermal is an impressive sight.