For video games, go with the Dawn of War series. The first game's campaign is a good intro to the mindset of the major factions and the universe as a whole. They're extremely well made RTS games to boot, so it's worth a look regardless.
As for novels, there are several good "starter" books. While the Space Marines are more iconic, I'd suggest you start with some Imperial Guard books simply because it's easier to relate to actual human characters. The Gaunt's Ghosts and Ciaphas Cain novels are the best of these, and some individual novels like Fifteen Hours and Gunheads are worth a look as well. If you want a slightly different perspective, Titanicus is an excellent book depicting the actions of Titan crews, and Double Eagle presents aerial combat much like if the Battle of Britain took place in the 41st millennium. As for Space Marines, the Space Wolves and Soul Drinkers series are good picks for contemporary versions of the current archetype. Crusade for Armageddon is fun in a pulpy kind of way, but the book's out of print nowadays. If wish to indulge your inner heretic, go with the Night Lords series.
Finally there's the book simply titled Space Marine, written by Ian Watson. It's been out of print for decades, but Games Workshop recently brought the title back on their Black Library website in print on demand form:
http://www.blacklibrary.com/Exclusive-Products/Print-on-Demand/Space-Marine.html
The book was written when Warhammer 40k was still young, when various elements of the universe were still being fleshed out. As such, there are some parts that aren't really compatible with the setting in its current iteration, and the book has been deeemed non-canonical in more recent years. This was also before Games Workshop started actively going after the teenage demographic, and this book is a reflection on that. Instead of being viewed as glorious "white knight" characters, the Space Marines in this book have the mentality of brainwashed child-soldiers raised in a horribly twisted parody of a "family." Despite their raw physical power, they are emotionally and psychologically fragile. They can even be downright psychotic in some cases. It's an unflinching look into just how warped the sensibilities of the Warhammer 40k universe really is. There are no "good guys," just varying degrees of harshness and cruelty.
I've actually never played the tabletop version nor do I have any interest in it, so you'll have to go by the recommendations of others.
As for novels, there are several good "starter" books. While the Space Marines are more iconic, I'd suggest you start with some Imperial Guard books simply because it's easier to relate to actual human characters. The Gaunt's Ghosts and Ciaphas Cain novels are the best of these, and some individual novels like Fifteen Hours and Gunheads are worth a look as well. If you want a slightly different perspective, Titanicus is an excellent book depicting the actions of Titan crews, and Double Eagle presents aerial combat much like if the Battle of Britain took place in the 41st millennium. As for Space Marines, the Space Wolves and Soul Drinkers series are good picks for contemporary versions of the current archetype. Crusade for Armageddon is fun in a pulpy kind of way, but the book's out of print nowadays. If wish to indulge your inner heretic, go with the Night Lords series.
Finally there's the book simply titled Space Marine, written by Ian Watson. It's been out of print for decades, but Games Workshop recently brought the title back on their Black Library website in print on demand form:
http://www.blacklibrary.com/Exclusive-Products/Print-on-Demand/Space-Marine.html
The book was written when Warhammer 40k was still young, when various elements of the universe were still being fleshed out. As such, there are some parts that aren't really compatible with the setting in its current iteration, and the book has been deeemed non-canonical in more recent years. This was also before Games Workshop started actively going after the teenage demographic, and this book is a reflection on that. Instead of being viewed as glorious "white knight" characters, the Space Marines in this book have the mentality of brainwashed child-soldiers raised in a horribly twisted parody of a "family." Despite their raw physical power, they are emotionally and psychologically fragile. They can even be downright psychotic in some cases. It's an unflinching look into just how warped the sensibilities of the Warhammer 40k universe really is. There are no "good guys," just varying degrees of harshness and cruelty.
I've actually never played the tabletop version nor do I have any interest in it, so you'll have to go by the recommendations of others.
