http://www.lttsolutions.net/ This is the protection i use you can pop it on a fair few times a year very quick and easy to use and results speak for themselves.
Two pics below first pic i took when i bought the Z Jan 2008
I think http://www.cleanyourcar.co.uk/ has already been mentioned, i've ordered loads from them and they're really helpful on the phone. Easier than Halfords IMHO
I think there're plenty of good products, it's down to budget and what you believe will work for you. Sites like clean your car give you a bit of info on the product, i also had a look at the manufacturers site and info on this forum.
A friend of mine uses autoglym products on his Porsche and is really pleased by the results.
Leatherique is the by far the best product I have ever used for leather. My e36 M3 was all hard and dried out (it's a winter beater so it sits most of the year unwashed and unloved). I finally decided to restore the interior and I'd be damned if it doesn't look brand new again... insanely good product.
I used the cleaner and rejuvinator. I bought some dye too but never needed it. Check them out their website has a ton of before/after photos of BMW's in the states that use this these products. Makes the leather nice and supple and not sticky. Seems to last a while too.
Even if you use a different product, they have some good how-to videos/instructions on leather cleaning/care/protection.
loads of stuff on the market, from experience, Swissvax cleaner is superb, Gliptone and Zainol also spot on, AG leather cream very good but can leave seats with a little more of a gloss than some would like, Swissvax leather milk is excellent as it tends to leave the seats with more of a satin sheen, whatever you use the age old phrase comes into play..........LESS IS MORE!