I've been playing some online games and reading "Overlord" (manga about an MMORPG) and slowly learning chatspeak so I'll start making a list of what I figure out here!

Last updated: 2017.09.20

こん茶：こんにちは good afternoon!
いてらー:　い[っ]てら[っしゃい]　see you later!
おは:　おは[ようございます] 'morning!
ノ:　乗る "riding" as in "i'll ride/hop on the bandwagon" = "i agree", "i'll come join the raid" etc. usually someone will ask something and then a string of people will "raise their hand" like this to agree.
あざーす:　あ[りがとう ご]ざ[いま]す "thanks"
イベ：　イベント "event", ex. キルイベ "kill event" (event where you're supposed to kill enemy soldiers)
サブ：　"sub" as in "sub-account, my non-main account"
アカ：　アカウント "account", ex. サブアカ "sub account", 新アカ "new account".
イン(している)：　ログインしている "is logged in" (インする to become logged in = to log on). note that instead of saying someone's "offline" they tend to just say "not logged in" (インしていない).
テレポ：　テレポート (アイテム) "teleport(ation scroll etc)"
引退：　"retirement" = quit the game (or guild)
神：　"god" = what you'll be called if you're online constantly, appear whenever someone needs you, or can translate between japanese and another language
kwsk：　詳しく　"in detail" = details/source please
w：　笑、笑う　"laugh" = lol
g：　ゴールド　"gold" (in-game money)
(お)ひさ：久しぶり　"long time (no see)"
萌え：　萌える "buds, becomes sprouting" but actually this is the kanji for "moe". Ex. ギャップ萌え "gap moe", the moe of a gap in looks vs personality.
ノンケ : ノンゲイ "non-gay", straight.
i am japanese! : this actually means "i only speak japanese, i don't understand a single word of what you're saying, slow down and be nice" etc.
native : too foreign/not japanese (as in "i only understand broken english, not authentic english!" = "too native lol i'm japanese lol").
モン:　モンスター monster
ハン:　ハント、ハンチング hunt(ing), ex. モンハン monster-hunting

General useful vocabulary:

同盟 "alliance" = guild (in certain games)
合併 "merge" = merging 2 guilds into one etc
兵士 = soldiers
切れ(た) = ran out of something, ex. スタミナ 切れ "out of stamina"
敵 = enemy
襲う = attacks, robs
敵襲 (=敵 襲う) = raid (enemy attacking you)
攻撃(される) = (become) attacked