I'd have to say Nippon Ichi.  Even moreso now that they're developing for Wii and DS. :)

Capcom - Shadown of Rome kicks ass...

 I like Resident Evil, Dead Rising (a bit) and some others from capcom too, so they are the best...

 BTW, I was wondering if some day I'll see another Shadown of Rome...        it would be great.

-Capcom: Resident evil 4... & Umbrella corp. Chronicles.

-Blizzard... Starcraft & Starcraft Broodwar.

-Suda51... No more heroes and 2 unnamed wii projects.

I like how No More Heroes and "two unnamed wii projects" made it on your list of favorite 3rd party games

my fav. is capcom, konami, and sega. I'm a bit old school like that.

for me it's namco, because of the tales-series and baten kaitos amongst other games.

but capcom, sega, square-enix and ubi soft all come quite close.

Capcom, Namco and Square-Enix! ^_^

square-enix, konami, and namco.

I love RPG, so it's easy for me right now :

- Square Enix

- Namco

Because the best one I've played are from these two. Well, seems like Sega is in too (for Skies of Arcadia Legends) .

Square Enix

Konami

Capcom

Sony

Namco

Nintendo (Miyamoto more like )

Ubi Soft

@ Diomedes: What part of: 'Which 3th party developer Do you like most?!' Didn't you understand... (Sony and Nintendo are called in your post)