For me this has to be:
1. Green Ronin Publishing: lots of well developed ideas, good grasp of the rules, constant level of quality - I hope they can keep it up

. This holds true for both, adventures (Freeport) and sourcebooks (Arcana

)
2. Fiery Dragon Productions: fine adventures with a fresh take on old concepts (I like their alert system), plus some nice illustrations.
3. Atlas Games: absolutely beautiful products (best art on an overall basis), good editing, nice ideas, though not flawless.
Additionally I'd like to mention:
Sword & Sorcery Studios: several exceptional sourcebooks (Hallowfaust, Relics & Rituals), a bit on the powerful side balance-wise, awful art, terrible maps


.
Malhavoc Press: nice take on core classes and concepts of magic
Well, I won't include companies with just few or single outstanding products (like Mystic Eye Games, Fantasy Flight Games) or those with much light and much shadow (like Mongoose).
Turjan