Not the cheapest option, but the CH Products Yoke and Pedals are a must have for anyone who's interested in realism.
The other FS 'must haves' are FS Navigator (so you can see airways, ILS beams, VOR's and generally orientate yourself) and Active Camera Pro which gives you the ability to move around the virtual cockpit - useful for visual approaches.
Finally, get yourself a few add-on aircraft as the default ones are a joke, especially the jets. The Level D 767-300 is acknowledged as one of the best as the attention to detail extends to the CC yelling at you over the interphone if you set the packs to too hot or cold! I'd also advise a good prop trainer, you can't go wrong with the Carenado Cherokee or similar.
Hell, while you're at it, get some realistic scenery for some UK airports from UK 2000 scenery so you can get the hang of where the taxiways and hold points are in real life. And the weather function in FS is crap so you'll need Active Sky for more realistic weather, and by the time you've got all this you'll need a £3000 PC to run it all...Still, beats an X Box
