Concept rockets?

Most of us are familiar with "concept" cars -- these are the one of a kind
vehicles produced by automakers as experimental projects, future products, etc.


I like the "concept rockets" that I see from time to time in various
publications, such as Discover, PopSci, etc. These are conceptual illustrations
of possible rocket vehicles, either proposed or in some stage of development.

For instance, the May issue of Popular Science had color illustrations of
possible launch vehicles for the proposed Orbital Space Plane.

Most of these kinds of proposed designs never make it into production in real
life, but they look like they'd be fun models! 

What do you think? Do you have any favorite "concept rocket" that never made it
into production? Do you think there would be interest in kits based on these
designs?