The IDW published GI Joe series is really good. It's not the cartoonish, aimed for kids, type of thing that may spring to mind if you aren't one to have followed the Marvel comics. This is consistently violent, anyone can die at any time (unlike the old series where you almost never saw that happen). Action, espionage, etc. It's worth checking out.
Btw, this does NOT mean the "A Real American Hero" series, as this is a continuation of the Marvel series. The new GI Joe is a reboot, but IDW publishes both.