Never use a leather... sacrilege.... Always use and dry with pure detailing cotton towels and while wet spray with britemax wax before wiping down.
The best soaps to use which some of the guys have already suggested are some of the Maguires products, anyone of those are really good, I use Maguires pre wash after I have double snow foamed the car. Also Britemax Grape shampoo if superb and is used by my detailer as one of the best. But if you want something a bit special but its not cheap is nanolex concentrate shampoo. Dont use this while it is really sunny but best results in dull weather. Only thing it does cost about £50 a bottle, the maguires are around £15 - £30 for 5 litres.
Take a look at the website
http://www.i4detailing.co.uk/ I order all my stuff from here.
Good luck