This is a video created by MetaBallStudios featuring a bunch of different sci-fi spaceships for size comparison purposes (previously: this giant insane chart verson). It is by no means comprehensive though so feel free to complain about how they left out your favorite spaceship. Do they not have any decency?! The rest of us will all silently shake our heads and judge you while you rant, and keep telling ourselves we never want to be like you when we grow up.
Keep going for the video.
Thanks to Brono, who told me it's not the size of your ship that matters, it's how you handle your crew. Okay is this about penises?