Most mangroves in the hobby are Rhizophora mangle, the red mangroves hailing out of Florida and the Caribbean. (Incidentally it has invaded a few spots in Hawaiian islands.)
I can talk a blue streak about the fishes and inverts you'll find here. Best place I know to send you is to the Smithsonian field guide (
http://www.sms.si.edu/irLspec/Species_Rpts.htm) A very high percentage of the species in those listings are mangrove forest inhabitants if not mangrove and seagrass edge inhabitants.
A few that come to mind, and that would be tank friendly (depending on the size of the tank in some cases)..
Mojarra
Striped blennies
Florida blennies
Mangrove blennies
Frillfin gobies
Alpheus sp. pistol shrimp
Libinia sp. spider crabs (though some get large)
Lookdowns
Threadfins
Mangrove crab / Fiddler crab *but need air
Gulf pipefish *special tank
Lined seahorse *special tank
Comb jellies (Ctenophora) *special tank
Upside down jellyfish *special tank
Seahare
Elysia sp. nudibranchs
Sheepshead minnows
Mangrove rivulus
Diamond killifish
Sailfin mollies
Northern searobin
Hogchoker (I think they get pretty big though)
As a slightly broader view of the definition, I often see juveniles of several species of reef fish going back and forth between seagrass beds and mangrove edges (but not mangrove swamps) including four spot butterfly, gray angelfish, and several of the Caribbean wrasses as juveniles.
In other words.. there is a
lot of life here.

If you expand out from the Caribbean it gets even more beautiful with archerfish, scat, and a zillion more.
I guess the question is really how big is the tank, how far do you really want to take the interpretation, and how big are you willing to allow the mangroves to grow before plunging into a biotope. The answers to these questions will help you narrow the field from any of the critters you find in research.
>Sarah