The biggest matches (in my opinion):
Borussia Dortmund vs. Ajax
Both still alive in the Group of Death, with Dortmund holding the inside track. A win today stamps BVB's ticket to the next round, but Ajax has proven a tough opponent. Big test for Klopps' crew, but one I think they'll pass.
Read Madrid vs. Manchester City
Amazingly, City is still alive, but they need to win every match and get some help. They'll be up against it today, going against Oezil and a motivated Real squad.
Schalke 04 vs. Olympiakos
S04 can also secure progress with a win. And they're at home, where they can be tough to beat. Even a draw helps Schalke, as their only remaining match is vs. lowly Montpelier.
AC Milan vs. Anderlecht
Not a battle of teams that might win the tournament, but still an interesting clash. A win for Milan puts them in great shape to advance, and helps take some of the pressure off of them, despite a tough season so far.
As always, try to keep it clean in the comment section. Happy Thanksgiving.