Pseudodragons have two dragon HD, which may just be the best type in the game. Their ability scores are reasonable for such a creature (-4 strength, +4 dexterity, +2 constitution, +2 wisdom). Their chassis also comes with considerable spell resistance, (somewhat limited) telepathy, a fly speed, blindsense, and two natural attacks (one of which has actual reach), as well as Weapon Finesse as a bonus feat.
Their sting is poisonous, though the fact that it causes sleep rather than unconsciousness is somewhat unfortunate: the DCs for waking up from noise are quite low, especially if there's still a battle going on. Then again, those few seconds may just be enough for the party warrior to CDG whatever went down.
All in all, this is a pretty tasty package, and obviously too much for a mere two RHD (which are, as I already said, excellent). I'm torn between +1 and +2 LA here, but for now I'll be going with +1, which makes pseudodragons reasonable rogue-types (albeit ones who sacrifice damage for utility).
Let the feedback commence!
Next are purple worms. I foresee -0 LA.