Probably the most common terrestrial isopod is the sowbug, or 'roly poly'.
Here are links to some awesome photos of various forms.
Isopod gallery
Isopods, Copepods, Barnacles, Amphipods, Sea Spiders, Horseshoe Crabs (Crustaceans) Starfish Photos
...and for the sci-fi fans like me, here's a photo of the giant marine isopod (up to 16 inches long!). When I was in grad school, one of the professors worked on these, so dried ones were all over her office and lab.
Giant Isopod - Deep Sea Creatures on Sea and Sky
Also, there are no 'bugs' in marine systems, but there are a few species of Pycnogonids (marine spiders).
Have fun!
Wendy