Dreams of Space. A blog featuring art from non-fiction children's space flight books 1945-1975. Lots of great graphics, from the realistic to the now fanciful. I must also point out the wonderful Czech pop-up book and A Trip to Outer Space With Santa.
Spaceships that became other spaceships: The Millennium Falcon, The Colonial Viper, The Eagle Transporter - from the blog of Gavin Rothery, visual effects designer on Moon. Previously.
Astrona - Space & Astronomical Art Journal : "specialising in space and astronomical art, science fiction art, visions of future worlds, design and visualization of technologies for living in space, space exploration, spaceships, starships, space colonies, etc."