Burakura (ブラクラ) - "Browser crusher", one who posts links to sites designed to crash users' web browsers.
Chu or Chubou (厨房) - An intentional misuse of kanji for "中坊" (a middle school kid), it refers to those posters who post without reading any rules, also to those who engage in flaming and spamming.
Fuun (( ´_ゝ`)フーン ) - a kaomoji for indifference; the word 「フーン」 is the Japanese equivalent of the English "hunh." The fuun face is the basis of the Sasuga Brothers AA.
Tsuri (釣り) - Trolling; a literal translation of "trolling" as a method of fishing.
Uho! (ウホッ!) - Originally from a gay manga, used somewhat like Haahaa and Kita!! but when the post is macho
w - A single letter substituting for "warai" or "laughing", added to mean that the poster is joking or thinks he made a funny remark, basically the equivalent to "LOL"; putting "wwwwwwwwwww" at the end of something is the same thing as saying "LOLOLOLOLOLOL". Also warota (ワロタ) from the Kansai-ben past tense of warau.