Steve Conley is one of webcomics' godfathers and while he's not unrecognized, he doesn't get nearly enough credit. Perhaps it's because he always had a different foot in different camps of comics. But just look at what he accomplished online this past decade. He self-published Astounding Space Thrills (and wrote a nifty bit of syndicating code); He started Comicon.com with Rick Veitch; and while serving as a judge for the 2004 Eisner Awards, he wrote the proposal for the inclusion of webcomics in the awards. Since then he's also had a couple years run mid-decade on Bloop, a sort-of spin-off of AST and the more recent opinion webcomic, Socks and Barney. He's also had a hand in several print comic projects such as IDW's Star Trek: Year Four. And this doesn't even get to his non-comics web resume.
As far as I can remember (and find from checking through the google-machine) from the beginning, Astounding Space Thrills existed both on and off the web. You can still read the webcomic archives online. The book collection, however, collects early issues of the comic book series. As mentioned before, Conley's strategy was to get the webcomic version of AST on as many sites as possible (remember this was before RSS feed creation tools were widely available) and so included a lot of links around each one of the online comics. But even so he managed to pack in a driving plot and action in those webcomics. Here's an early one including a bit of animation in the second panel. It helps to remember too that Conley was working within the bandwidth constraints of that era and so he was always trying to keep the file size small. He still has a page up on how he created those first webcomics. Conley eventually produced over 350 of this version of the webcomic.
The comics in the book are similarly fast-paced action-oriented tales. Conley's strengths here are the artwork, which is mostly black and white with blue-gray tones throughout (the last story and covers are in color). It's great line-work, interesting character designs (especially the character of Theremin) and generally Conley's visual sense is impeccable — you're moved along but never confused as you read through his panels. Conley's been pretty consistent in describing AST as a homage to cheesy science fiction serials like Buck Rodgers and it definitely delivers on throwing in all kinds of science fiction and fantasy tropes: dinosaurs, a version of hyperspace, crazy villians from space and other weird aliens. I liked "The Secret of Mooch's Loot" the best — Mooch is the one authentically funny character in the comic and it lends a kind of crazy hijinks tone to the whole proceeding that elevates it over the other stories.
The book is still available through the AST website (with Conley's signature) for $20 (+$4 for shipping). I bought mine at a bookstore (or maybe it was the Cartoon Museum in San Francisco, CA; can't recall right now). It's a quality book and has the bonus of being relatively all-ages appropriate; I really can't recall anything in it that's actually scary or disturbing. It might still be PG as opposed to G but I think most kids would do fine with it.