As a follow-up to my earlier post on the Starship Comparison Poster, the Starship Dimensions website has a much more extensive library of sci-fi ships all shown to scale. There are so many here that the website is broken up into different pages from small scale up to "Big" scale. Click on the tabs across the top to pick a scale (100X, 10X, 1X, etc.).
Fantastic resource. Jeff Russell has done a great job accumulating the images and tracking down their relative sizes.