what sort of money are you looking at spending, have you a line in the sand for age or signs of use, what sort of riding options, gearing, suspension, compactness of fold v ride ability?
No, if you want to be cryptic and unhelpful then best of luck with others.
I have a Brompton Superlight (titanium forks, rear triangle, seatpost) upgrade to 8 speed Sturmey Archer hub gear, with Brompton S-bag and bike cover. Low mileage.