Clark Lindsey lets us know about Marcus Lindroos' archive about "future launch vehicle" designs that arose between 1963 and 1993 (the intro says through 2001, so I assume there is more to come). Here are the top-level categories:
1. Early American Reusable Launch Vehicle Proposals (1963-67)
2.THE SPACE SHUTTLE -- From Dream to Reality (1968-72)
3. THE 1970s -- Solar Power Satellites and Advanced Launch Vehicles (1973-80
4. NASA "Shuttle II" Advanced Manned Launch System studies (1978-89)
5. Military Spaceplanes (1978-93)
I haven't looked through the site much, but it should be a good resource. The intro page provides a convenient slide-format presentation of the material on the site. On the down side, the images aren't appearing for me in-line so causal navigation is cumbersome.
I foresee a new section on the one and future Ares line of vehicles. Other than the Ares 1-X, these may forever be stuck in the 'future' category.
BTW, the photo is of Quest's Future Launch Vehicle (which isn't included in the archive).