Brett is often referred to as Mr. Brett. His nickname for years has been “Starbolt”. He used it when he joined IRC. In the liner notes of Suffer, No Control, Against The Grain, Generator and other albums by other bands, one can read “engineered by the legendary Starbolt”.
His nickname on the Internet is "Oblivion Pact" (e.g. on Flickr, Twitter, last.fm). On MySpace, he is "brettosis". Brett is meant to be Billy in the song of the same name as well as Billy Gnosis in the eponymous song. He is credited as Billy Pilgrim on The Seeing Eye Gods.
Brian’s nickname on message boards usually is “BB” (also here on TheBRPage). On MySpace, he is "pilgrimdoss" a.k.a. "SENOR TAPAS".
Brooks’ nickname is “b-wack”. On MySpace, he is "jakeeasy" a.k.a. "brooks".
Greg’s nickname listed in Cornell’s Network Identity Directory is “Aludensparglemein”. The directory also describes his activities in the college as “Investigations into the origin of bone tissue, and travelling”. The nickname doesn’t mean anything in particular. On ICQ, he used to have been “gerg”. It is also believed that he used/uses the name "Graffinius".
Jay’s nicknames on message boards are “jabberwock” (under which he posts here on TheBRPage), “niblick”, “jdb”, "geust", "chud" and "Yeust" (which he used on the old chatroom and first message board from the now extinct official site).