I second the B&W Nautilus and Diamond series Speakers. Even after 7-years, used B&W Nautilus Speakers are sell fast usually within a week at more than 50% of their original retail value. When you consider that Krell and JM Lab/Focal Speakers can be bought new at near 50% discounts this is a pretty amazing statistic.
Top resale value speakers
When you consider buying a new pair of speakers, the sound, outlook and review of the speakers are important, but resale value of speaker is also a important thing to consider before your purchase. Some of the speakers resell value drop so deeply, but some don't. Can you suggest some high resale value speaker company? As far as I know, B&W have a pretty strong resale value compare with their brand, such as Dynaudio, Proac or JMLabs.