Off the top of my head...
HW:
Cain vs. Overeem (after Overeem beats Bigfoot; actually, this would be a super fight in a way)
JDS vs. Cormier (once Cormier comes to the UFC)
The winner of Cain/Overeem vs. Werdum
JDS vs. Overeem
JDS vs. Cain III (for this and JDS vs. the Reem, one would be a title eliminator, the other a title fight)
Sylvia vs. Arlovski V-LXVIII (kidding!)
LHW:
Jones vs. Henderson
Jones vs. Machida II
Machida vs. Shogun III (if Shogun gets fully healthy and goes back to being, well... SHOGUN!)
Teixeira vs. Gus
Rashad vs. Machida II
Davis vs. Gus II
MW:
Silva vs. Belfort II
Silva vs. Bisping (to shut up Bisping)
Belfort vs. Weidman
Weidman vs. Bisping
Lombard vs. Weidman
WW:
GSP vs. Hendricks
Koscheck vs. Fitch
Condit vs. (UFC 153) Fitch
Condit vs. Diaz II
Koscheck vs. Kampmann
Kampmann vs.
LW:
Pettis vs. Bendo II (if you don't want this, there is something wrong with you!)
Melendez vs. Bendo
Alvarez (come to the UFC?) vs. Miller
Alvarez vs. Chandler II (because the first match was nothing short of amazing)
Chandler vs. Lauzon (doubtful, but it sounds awesome!)
Lauzon vs. Diaz
Aoki vs. Alvarez III (another very unlikely fight, but it would be so cool!)
Melendez vs. Cerrone
Melendez vs. Miller
Diaz vs. Maynard
Maynard vs. Cerrone
Cerrone vs. Lauzon
FW:
The winner of Aldo/Edgar vs. KZ
Curran vs. Mendes
The winner of Lamas/Koch vs. Mendes
Swansom vs. Poirier
KZ vs. Poirier II
Poirier vs. Garcia
Anyone vs. Guida... as long as Guida gets knocked out!!!
BW:
Dominick Cruz vs. someone this year
The winner of Barao/McDonald vs. Wineland
Faber vs. Wineland II
Pickett vs. Jorgensen II
Assuncao vs. Jorgensen
Pickett vs. Assuncao
Faber vs. Assuncao II
FLW:
Benavidez vs. Dodson (this fight sells itself)
McCall vs. Dodson
Dodson vs. Moraga II
Mighty Mouse vs. McCall III (I love a good trilogy)
Mighty Mouse vs. Benavidez II
Montague vs. McCall II
da Silva vs. McCall II
Montague vs. da Silva
Gaudinot vs. Moraga
Champion vs. Champion (as we all know these are pretty unlikely, a few cases aside):
The winner of Aldo/Edgar vs. Henderson (or Pettis) for the LW belt (not too unlikely)
Dodson (if he beats Johnson) vs. the Barao/McDonald winner for the Interim BW Title (very unlikely)
Chandler vs. Askren/Curran (even if you don't like Bellator, that would be must see MMA!)
Chandler vs. Melendez (Bellator Champ vs. Strikeforce Champ! It would make a great eventual UFC LW Title Eliminator match!)
GSP vs. Hendo (two great wrestlers; pretty much impossible, but I would enjoy it)
Silva vs. GSP (herpa derpa; not gonna happen this year, but one can hope; just don't count on it)
Cain vs. Jones (this is looking more and more like a possibility for 2013-2015)
Jones vs. Silva (very unlikely for this year, but let us hope it happens sooner rather than never!)