Microsoft for sure. They have lost too much momentum, and most of the debating around the boards at the moment is Wii vrs PS3. We all know Sony has some great games arriving, and the PS3 is just warming up.
This will be the 3rd Xmas(!) for the 360, and its make-or-break time IMO.
What MS need:
1/ Most important, eliminate the "RROD" 360 issues. Announce a new model (or 2), free replacements for everyone, and that the issues have been completely fixed. Until they do this, I can't consider picking a 360 up.
2/ Show lots of Halo 3, and blow people away. Too much shown for the game has been mediocre at best.
3/ Announce some awesome exclusive content (i.e. a FF title, or MGS hitting 360 this Xmas). Mass Effect, Too Human, Fable and more.
4/ Push the GTA4 angle, with exclusive content.
5/ Announce a price cut.
...
All Sony need to do is show videos for their announced titles (Uncharted, LAIR, etc..).
Nintendo just need to keep doing exactly what they have been - a couple of unannounced titles would be cool though. Some Wii RPGs are needed. I'll be very happy if they announce a new handheld (GC portable), as well as better storage system for the Wii (better SD usage at least).