Pretty much what the title says.
Pick one fighter from each major division, HW, LHW, MW, WW, LW, FW, BW to come to the UFC (I realize you probably are thinking more than one, but try to just pick 1). They could be a fighter that has previously fought in the UFC that you would want back.
The person doesn't necessarily have to be a title-threat immediately and may just be a very exciting fighter.
I got this idea from my dad who I got into MMA a few years ago, so pick away!
I'll start:
HW - Barnett (I'd like to see him in some battles with the likes of Mir, Nogueira, even Lesnar)
LHW - King Mo (Love to see how his wrestling, and overall technique, holds up with the top of the division)
MW - Hector Lombard (Give him some top guys and see what happens)
WW - Ben Askren (how will he stack up against experienced/high-tier ww's?)
LW - Gilbert Melendez (Pretty much the most obvious choice, don't really need an explanation)
FW - Patricio Pitbull (He is a killer, with growing experience he could turn into a star)
BW - Zach Makovsky (I really enjoy watching this kid fight and think he could turn into a force in the division)
HW - Glover
LHW - Feijao
MW - Falcao (bring him back!)
WW - Lima
LW -Freire
FW - Freire
BW - Dantas 
Ww dayley
Hw werdum
Lw Melendez
FEDOR TROLLOLOLOLOLOL :P
HW - Comier
LHW - Mousasi
MW - Rockhold
WW- Satoru Kitaoka
LW - Aoki
FW - Kawajiri
BW- Bibiano Fernandes
Barnett, mousasi, jacare, askren, Melendez, freire, makovsky
Thatsjustlikeyouropinionman - Hw - Sylvia (yea, I know)
Lhw- renato
Mw- kendal grove
Too drunk and high to finish this list
Drunk at 6 est? My god
Hw: Barnett
Lhw: Mousasi
Mw: Lombard
Ww: Daley
Lw: Melendez
Fw: Pitbull
Bw: Zach Makovsky
HW - Guram
LHW- Vinny
MW - Lombard
WW - Askren
LW - Melendez
I'll stop there as I don't follow the two smaller weight categories that closely anymore.
HW: Fedor
LHW: Mousasi
MW: Jacare
WW: Askren
LW: Melendez
FW: Kawajiri
Hw:fedor
Lhw: king mo
Mw: falcao
Ww: Nate
Lw:Gilbert Melendez
HW: Minowa
LHW: Minowa
MW: Minowa
WW: Lyman Good
LW: Masvidal
FW: Crusher
BW: Imanari
behrens14 - HW - Comier
LHW - Mousasi
MW - Rockhold
WW- Satoru Kitaoka
LW - Aoki
FW - Kawajiri
BW- Bibiano Fernandes
Cormier would wreck the heavyweight division IMO. He is the second coming of Fedor.
HW: Fedor Emelianenko
LHW: Keith Jardine
MW: Hector Lombard
WW: Ben Saunders
LW: Rene Nazare
FW: Tatsuya Kawajiri
BW: Mazakazu Imanari
Fedor
Mousasi
Lombard
Daley
Melendez
Pitbull
Dantas
HW: Barnett
LHW: King Mo, just for the rampage fight really
MW: Was Michael Falcon, but since Id rather see the man live healthy after his scare. Jacare in a bjj war with Demian Maia.
WW: Askren, let's see if he can hang with the big boys.
LW: Although Aoki and J-lau would be a fun ground fight, I'd rather see Melendez vs Edgar/Benson.
FW: Curran, would have said Sandro but Pats got the win on him.
BW: McCall, just because I wanna see Uncle Creepy in the UFC and until they bring 125ers in, I guess this is the only way. 
HW: Fedor or Black Fedor
LHW: Jimi Manuwa
MW: Tom Watson
WW: Daley