I haven't had a lot of free time, but I get to see Roppongi (and Midtown) since I go there for work sometimes.
Been to Shiodome... plus a few other smaller spots.
I used to like the Shinjuku Southern Terrace lights, but this year... they've got all pink/purple lights and no real christmas display. Or, maybe they haven't put everything out yet. Takashimaya department store was also lacking this year...
Tokyo Dome City has some, as does Marunouchi... I'm interested to see if Odaiba has some nice lights this year.