Did a quick check.
War of the Burning Sky. If they're running the full thing, it starts at 1st level and goes to 20th.
So, to start:
Strongheart Halfling Druid 1
Wis->Con->Dex->Int->Cha->Str
Feats: Greenbound Summoning, Improved Initiative; if flaws allowed, add on Ashbound (page 50, Eberron Campaign Setting) and whatever you want; hell, set a feat on fire for a prereq.
Put some points into Ride early on so you can ride your dog AC and negate attacks with your Ride check, possibly wielding a Small Lance. Spontaneously rip out doubled duration, auto-buffed plant-animals to throw down Entangles that last longer than what you can cast (1/round HD duration). Own tremendous amounts of face.