A simple human, half-orc, elf, or dwarf druid with various Wild feats and such can be pretty effective and versatile. Learn to make the most of Wild Shape and various druid spells, use Wild feats and the feat that lets you cast while Wild Shaped, and take some general-purpose feats like Lightning Reflexes, Improved Initiative, Combat Reflexes, or something. Druids are masters of information-gathering, exploration, and burning stuff.
Could be rather useful. A half-orc or dwarf druid could be fun to play. Emphasize mental stats and maybe Constitution when assigning ability scores, and rely on Wild Shape forms with Greater Magic Fang when you need to fight in melee. Druids can use Produce Flame, Heat Metal, Chill Metal, Flame Strike, and such for ranged combat when needed.
Some of the character concepts you mentioned just don't seem to me like they would mesh well with the group-as-described, or with the type of campaign (dungeoneering and investigation). Goliaths are overpowered anyway from what I've heard, and some of those races you mentioned would probably be counterproductive when trying to deal in town, where folks would be intimidated, disgusted, or frightened by the character's race. Druids eventually gain A Thousand Faces anyway, which allows them to mimic the appearance of various humanoids at will. Might not want to out-shine the rest of the group in combat, or you might get a rude reception or something, and some of your concepts look like they'd pretty much be geared towards annihilating stuff quickly rather than working with the team or roleplaying. The Shifter prestige class (apparently renamed Master of Many Forms?) is quite capable of breaking the game or at the very least presenting a whole slew of problems and challenges to the DM that will make his job far more difficult than it should be (and much more trouble than it's worth). Likely why he didn't approve of that concept when you first presented it.
Prestige classes are entirely up to the DM as to whether or not they will be allowed. Anyone who thinks that the DM should allow just anything printed in a WotC book, without reservation or consideration of the campaign setting or the other players, is a clueless fool. I've seen many a game dominated and ruined by one obnoxious or cheesy player who used some prestige class, feat, or spell from a supplement that was just entirely too overpowered, abusive, or complicated for the DM to handle. I limit the PrCs available in my game based on what's appropriate to the campaign setting I use, and according to my experiences and analysis of the material as to how fair it is or how difficult it may be for me to account for in the game.
