I was about to say, I don't really give a crap about brands in general. I find it absolutely mind-blowing that people will spend £1000 on a £5 pair of trainers because they have a gold tick on them or whatever.
The thing I've found most awesome in second hand stores is leather jackets. You can pick up a leather jacket that would cost you £200-300 new (or even more) for like £15. And they're usually in excellent condition too, because they don't wear much and can be restored fully with a little bit of effort anyway.
I've got a badass black leather jacket I got used and I usually combine it with a snug-fitting t-shirt underneath, gives me a muscular "biker" look that I personally dig. Combine it with shades and you'll have people literally commenting that you have "style". I think because it's a strong masculine look and people are so used to bearded skinny hipsters wearing denim it really makes an impact.