Just wanted to say, in case anyone's missed it, that Mare Internum by Der-shing Helmer has come back from its hiatus! You may wonder why this needs to be in a post on here, but once you've read it you'll understand. It's probably the best webcomic that I've read, and anyone who's interested in hard sci-fi should give it a go!
Basically, it's a character-driven story about two astronauts trapped in a subterranean sea on Mars. The way this world is explored, and the way the characters are delved into is such a fascinating and moving experience. So, yeah, I know this is kind of spamming the forums, but seriously, you need to read this!