A couple of ideas for titles:
A Swamp Environment book? "Quagmire: Mastering the perils of Marsh and Fen"
Forest/Jungle "Briarthorn: Mastering the perils of Woods and Wilds"
A Plains book? "Meadowsquall: Mastering the perils of Winds and Plains"
Despite the images these names bring to mind, I can't find myself being terribly enthused with the notion of additional environment books...truth be told, the "races of" line has done a decent job of filling in the gaps. Races of Stone is a mountain and underground book, Races of the Wild is a forest/jungle/plains book, and Races of Destiny is frankly more of a City book than anything else.
I think that the idea of the environment books was to showcase environments that are "wastelands", not only in that they are difficult to survive in, but in that they are not used very often in the D&D Euro-centric archetype. Deserts, Glaciers, and Seas were all impediments to Midieval travel and settlement and "exotic" locales frought with danger. True, mountains and plains and forests and jungles also pose such threats to human advancement, but you have to consider that D&D does not operate on the assumption of all Human PCs. Going deep underground or up onto a mountain may be frightening or exciting for a human PC, but a Dwarf will be right at home, and take it as a matter of course. Likewise, forests and plains are hardly an exotic notion when you have Elves, Halflings, and Half-Orcs who all make their homes there, not to mention the fact that the Druid and Ranger classes seem designed with those locations in mind.
Simply put, a Frozen Glacier, a Blazing Desert, or a Storm-tossed Sea are not natural environments for any of the PC races, and are truly "exotic", while the other environments are simply "home" for one or more PC races, which makes them seem mundane to at least some portion of the (theoretical composition of) a D&D party, and thus not really worth writing a book about without making it about the means by which those races make it home.
Robert "My Two Cents" Ranting