I need a good username (If i chose your, you will get a item from my inventory)

Zange
ZarteZange :^)

Zoozan (sounds like susan lols) Z-Axis TargetZan I unno made it up, ZoomlenseZan or Zoom-Lense-Zan or Zoomlense-Zan ZanZooms that it for now or i'll be here all day =p.

Zamazing :D

Zhukuchi

I know that the real word starts with a S, take a look at the description of the word and it will be the best name for an assassin. (Also, one of the skills of a dota character)

Oh my god I looked at so many words with Z it doesn't look like a letter to me anymore...

I'm surprised nobody said Zangetsu.
You could also go for Big Zan - a nice gundam reference, if you're into that.
If you're not, you could try Zeddozan or Zannaz. The beauty of Zannaz, you see, is that you can read it from left to right as well as right to left. Anytime anyone asks you to spell your name backwards, you just have to spell it normally! Quite genius if you ask me. You could try Zoddoz for the same effect, but then it wouldn't have the Zan.

ZANta Claus

Zantetsuken.
Zanmato?
Zany.
Zandstorm (Sandstorm)
Zandyman (Candyman) - You can tell I'm running out of ideas.
Zandy (Candy/Dandy)
Zandylion (LOL. Sorry about this one.)

And a bad pun that doesn't start with Zan.
Poizand. (Poison)
QuickZand (Quicksand)

Zangerous Zan
Zantastic!
ZombieZan (I presume this has been already posted buy I've have not seen it yet)
and...
Zond, Zanes Zond

Zanzibar
Zan216ar
Zanz1bar
Zanz16ar
Zan21bar
Zan2i6ar

Zanoric
Zanbor
ZanZan
Zanarry
Zanumba
Zanic
Zanix
Zane
Zanter
Zantex
Zanrex
Zanray
Zanpam
Zamazan
Azanis
Azozan
Azanx
Blizzan (I kinda like this one :p)

edit:
Suzanne
Wizann
Hezan
Izan
Lorzan
Trizzan
Xorzan
Klizan
Slizando
Zanlando
Quezan
Arzang
Tezang

Zarcotzan

zanit

Zan FranCSGO (San Fransisco)
Zlatzan Ibrahimovic
ZannaZ

Zanzatan
Zanarix
Zinkozan
Zetazan
Zazan

zangieff

BoldZANTheBeautiful [my favourite]
ZboldZAnZbTful
ZAN Perrion
ZANzoROTARY
ZAN-ZO-ROTARY
ZAN Gula
Count Zangula

Zandarrion. Zan Zebastian, Zan-Kor, Zanizzian, Zanzoom.

zan-zaaz

BlackZan or Zannihilator or KinZang or aZanner or Zansaber. Pick one of this please and give me a key :D GG buddy add me on steam i play csgo

Zanix
Zandanix
Zirazan
Zanexxe
Zanoke
Zezzan
Zirdazan
Zerzan
Zizzanix
Zozane

(Not sure if you meant just Zan in general, or ZAN in all caps, but these work with either :p)
That's all I have for now :p

Zanzei
iZan
Ozan
ZoZan

ZAN ZAN ZAAAAAAAAAAAN! Like this tune

Zanderman (thunderman)
Zan Zan
Sr. Zan

Zantetsu
Zanbi Asu
Zankyou no Shi

hmm.. the good thing about Japanese is that it has quite a few "Zan" sounds. The bad news is that they're not particulary good names for gunmen, so not really the best for FPS'es in general.