Sorry I posted just one review... I haven't had much experience
with the others with the exception of the Sugar Shack. I also
included websites so people could get a good idea of what the
places look like and what they serve.
Crab Shack: http://www.thecrabshack.com/
These have been robbed from other places on the net...
North Beach Grill
Sandy feet are always welcome at this lively pub and eatery just off the beach. Tybee Islands historic lighthouse looms overhead as plates of oysters, locally-caught fish and hometown favorite crab cakes are spread in abundance. A strong Caribbean influence runs through much of the menu, so if you like it spicy, you're in luck. Dress may be a little more elegant than at some Tybee establishments, but that is the extent of formality here. The adjacent bar stays open late most nights.
Sugar Shack, conveniently located on Highway 80. Although there are menu items for breakfast, lunch, and dinner, the fresh peach milkshakes and brown cows are the best. A brown cow is a delicious twist on a chocolate milkshake: chocolate ice cream and vanilla syrup instead of the usual vanilla ice cream and chocolate milk.
Bubba Gumbos web: http://www.bubbagumbos.com/
Bubba Gumbo's restaurant serves both lunch and dinner. A selection of seafood and regional specialties are served for lunch. Hamburgers, chicken fingers and pizza are served on the children's menu. A seafood buffetis available for dinner and a full menu is also offered.
The Breakfast club.. (which I've been told to include)
http://www.tybeeisland.com/dining/brclub/
Full review : http://www.savannah-online.com/full_story.cfm?sect=TourismDining&id=601
For people that have never been to Ti/S: Someone mentioned
an Arby's on the island. Let me just go on record and say that
the FastFood in and around Savannah is bad, really bad. How
bad? Like 20 minute waits, messed up orders, apathetic staff,
and bad food.

I know that fastfood can be that way
anywhere but for some reason it is particularly bad here.
So just stick to local resturants if you can. Just to warn ya...