First of all, hope I'm not breaking any rules regarding advertising here, I am in no way associated with this company or gaining anything by writing this, but:
I'm sure most of you (in the UK anyway) are familiar with Autoglym products. I've used them for the past 4 years on my 318ti and been very happy with them.
Recently I noticed they'd released something new called Ultra Deep Shine, aimed at dark coloured cars. Seeing as my car is Cosmos Black I'd thought I'd give it a go. Spent a few hours tonight cleaning like mad and I have to say it is incredible. My car is now so shiny, the only way I can describe it is to say it looks like it's permanently wet, phenomenal stuff, especially as my car is over 7 years old.
Again, apologies if I shouldn't be highlighting an individual product, but I'm so impressed with this stuff I had to recommend it. If you've got a dark car that needs refreshed, I can't recommend it highly enough. ;-)