Ray Gun (MKII)/S&M (M&S) - Always a solid choice. Very powerful and, when combined with PHD, can help you escape from many near-death situations. Even without PHD, they Ray Gun is probably one of the best weapons out there (along with it's counterpart, the Mark II).
Galil/SCAR-H/M1927 - Unless I have Deadshot, I find myself often hip-firing for headshots. It's quicker than ADSing, and seems a little less dangerous at times. All three of these guns are pretty good for that, with emphasis on the Galil, as it has slightly better hip-fire accuracy (though slightly lower mobility, as well).
M908/HAMR- Plenty of ammo (100/400 and 125/375 respectively), fairly mobile, and has very nice sights. They are both very similar to each other, though I prefer the MG09 because of the HAMR's recoil pattern (if I remember correctly, it pulls up and to the right when fired).
Gersh Device - As far as tactical grenades go, these are simply insane. They suck in the zombies while activated, plus you can jump into them to warp to a random location. Fancy.