OK, here's my "real world" list:
CAR-15 (of some sort, whatever tickles your fancy): military, police, civilians all have one so parts, mags, ammo should be readily available after the apocalypse hits
Remington 870: lots of ammo, spares available
Remington 700, .308: accurate, reliable, ammo readily available
Ruger 10/22: lots of ammo available, everybody's got one, accurate, reliable, hunt small game (woof! meow!). Might prove powerful enough against small zombies like Sofia
S&W J-frame .38: never know which ditch might be the last
S & W 5906: there's bound to be lots of spares, parts, mags, holsters lying around once the apocalypse hits
Beretta 92: same as above, only gotta scrounge on base
Colt Series 70 Government Model .45: only because I love that gun!
Now, if there were no restrictions on what you could have:
M-4, full auto with suppressor
10/22 with suppressor (still gotta eat)
Browning .30 MG air cooled with truck mount (ala Somali "tacticals")
H & K MP5SD
Remington 700 .308 with suppressor
S & W J-frame .38
Suppressed Saiga 12 ga from Red Jacket
Colt Series 70 .45
Lots of emphasis on suppressors since zombies are attracted by loud noises.