The easiest - and true Turbo Cider - is apple juice, and yeast. That's it. I use Young's champagne yeast, which gives a VERY DRY cider at around 6%. I am going to try their cider yeast this weekend as an experiment.
This basic recipe tastes a bit rough and ready though. To make it nicer, use just under 4.5L of apple juice in a demijohn, then add 1 cup of overstewed tea (use 5 tea bags and stew for 15 minutes) and 1/2tsp of glycerine. The Glycerine is available from all chemists. DON'T ADD TOO MUCH - 1/2tsp is PLENTY. Top up to the shoulder with more juice if you need to close the gap.
In order to see what difference it makes, make 1 demijohn with just juice and yeast and another with the tea and glycerine added. Ferment until ready and no more bubbles, then condition in bottles with 1/2tsp of sugar in each to prime and carbonate your cider - if you like it fizzy that is. Any more sugar than that and you could blow the bottles so measure carefully. Grolsch swing-top bottles are superb - they sell them in large ASDA stores.
Leave the bottles in a warm place for 4 days or so to get the secondary fermentation done and then bung them in the garage or some place cool for 10-14 days to let them condition and carbonate properly. The longer they are left, the nicer they get but 14 days is fine and means you can sample them quickly!
I hope this helps - do let us know how you get on.
