Well, I like the drakes so far, in any case. I mean, yes, they are powerful, but is not like they can solo a elephant or anything.
A few ideas for further expansion:
River Drakes are kind of like a smaller, meaner whiptail. Has a nastie little breath-weapon that causes suffacation if it hits the bloodstream. Large, almost swarm-like packs.
Rage Drakes are like meaner, harder-to-fight wolves, and come in two flavors: a small-ish one with a mild toxic bite and a rarer, bear-sized one without the nasty bite attack.
Sandstorm Drakes are bit like a classical wyvern, with a tail with a nice, sharp blade at the end with or without a deadly nerotoxin. They have wings but cannot fly, and I would think they use them to drag themselves across the desert like a grounded bat would. They behave like vultures do currantly, but not like that realy matters when you end up in a evil desert and it keeps reanimating itself.

Deep Drakes are the degenrate kin to the Cave Dragons. No upper limbs, a nice inherent Bite skill, and functinal wings, and you have the natural hunter of giant bats (and ignorant dwarves). Goblins would probably get a chance to ride these guys.