2. Rapid Decompression
Most people have heard of "the bends," that condition that deep sea divers get if they resurface too quickly - another Hollywood staple. Officially known as decompression sickness, this condition occurs when your body suddenly moves from a high-pressure environment to a low-pressure one. The lower pressure causes dissolved gases to expand into bubbles inside your body, and depending on where these bubbles form, the results can be fatal.
Since space is a vacuum, it is the lowest-pressure environment imaginable - there are no air molecules, so there is nothing to exert pressure on your body. While that doesn't mean you would explode, like some movies would have us believe, it would lead to swelling. Human skin is sturdy and elastic enough to prevent us from popping like a balloon - Total Recall's inflating heads may be an exaggeration.
Rough estimates suggest a human can survive for up to 90 seconds in a vacuum, but would lose consciousness after about 15 seconds. This ties back to asphyxiation - the low pressure outside the body would cause oxygen to rapidly leave the blood. And if you tried taking a deep breath before hopping out into space, your lungs would likely pop during the rapid decompression, since they've already expanded as far as they can go.