Andalites: They can move and strike fast. They're very diffucult to sneak up on, unless it's dark or something. They also have thoughtspeak. Should morphing count, since it's not a natural ability?
Hork-Bajir: A destructive force, but with a peaceful attitude. Speak softly, but carry a big stick. Very good climbers.
Ketran: Maybe a few too many appendages, but it's a sentient bird species. Not too bad.
Howlers: These guys are even more wicked than Hork-Bajir, and they have collective minds.
Yeerks: On one hand, their bodies are nothing impressive. On the the hand, they can control almost any sentient creature, and a few nonsentient ones.