Aeolius
Adventurer
That looks interesting, but it also looks as though I'd have to pay for it, which I can't afford unfortunately.
I really enjoy creating settings and worlds for things anyways though, and I find I'm generally more comfortable using worlds I've created as a setting than I am using someone else's setting. Doing it this way is a lot of work, but I'm looking forward to the eventual completion of my project.
The PDF of Cerulean Seas is $19.95, which for the amount of information presented is quite a bargain - never mind the absolutely stunning illustrations. If you are familiar with "The Deep" by Mystic Eye Games, Cerulean Seas has a similar feel to it.
While on the topic of worthwhile investments for an undersea adventure, I always recommend Discovery's Blue Planet series ($14.99 on iTunes / $39.99 at Discovery), and DK Publishing's [ame="http://www.amazon.com/Ocean-American-Museum-Natural-History/dp/0756636922/ref=pd_sim_b_2"]OCEAN[/ame] ($18.45 at Amazon).
Though, if you're on a budget, I'd recommend the Monterey Bay Aquarium website. Their webcams are simply mesmerizing.