I actually wote up a series of feats for the PHBII "shapeshift" druid that would grant new forms -- I think I went with "Stealthy Stalker", which was a rat or cat or some similar thing (you shrink to Tiny, bonus to dexterity, and... Eh, I can't remember wtihout going to look it up). Another was the Aquatic form, which had Flier as a prereq and let you become a dolphin or otter or some similar air-breathing swimmer -- granted a swim speed, con bonus, and the ability to hold your breath a lot longer (10x, I think, to "one minute per point of constitution").
I think I wrote up some others that aligned to the other forms, but I don't remember what they were except for the Massive Beast form, which gave a trample attack and turned you Huge, to represent an elephant or large sauropod dinosaur.