This is a list of every -tan and -chan that I came across in my 4chan /b/ 2006-2008 archive.
Nevada-tan/-chan - A twelve-year-old girl who slashed the throat of her classmate with a box cutter. She is called Nevada-tan because she wore a Nevada sweater in a class photo and received a cult following online. First known reference here.
Rabbit-chan - Woman with flat chest. First name thought to be Caitlin. There were many threads made about her and she was referenced a lot in many threads during early-mid 2006. In one thread it was stated that there was ".zip of rabbit chan pics". She was once even said to be the "heart and soul" of /b/, but also "worse than Desu" in the same thread. A list of all threads about her is avaliable here. A small collection of images of her is here.
:3chan - Very Cute.
Hermione-chan - Mina Suvari from American Beauty, who happened to look like Emma Watson with heavy makeup.
Flat-chan - Flat chest.
Loli-chan - Loli, obviously. Said to be important to 4chan.
Magic-chan - Apparently looks very geeky. Disliked by majority of /b/, worshipped by a few people. Said to actually a fat man pretending to be a girl, but this is unconfirmed. It was also once said that her teeth were disgusting. Original thread here.
Neko-kun - Presumably a cat/furry boy.
Togi-chan - A woman with a fat ass. A collection of images of her is here.