[3] The first project MonkeyBrain Books published was a collection of companion notes to Alan Moore and Kevin O'Neill's 1999 comic book series The League of Extraordinary Gentlemen, Volume I: Heroes & Monsters: The Unofficial Companion to the League of Extraordinary Gentlemen, compiled by Texas-native Jess Nevins.

[4] It was nominated for an International Horror Guild Award and favorably reviewed in both Locus and The Magazine of Fantasy and Science Fiction, among other publications.

[5] The companion to The League of Extraordinary Gentlemen, Volume II followed in 2004, and in 2006, Titan Books published the UK versions of both titles.

Continuing its self-imposed remit to publish works of non-fiction genre studies, MonkeyBrain's debut titles (in December, 2003) also included a collection of short essays by Matthew Rossi, comprising a wide-ranging guide to numerous weird, odd, imaginary, and mythical places and things: Things That Never Were: Fantasies, Lunacies & Entertaining Lies, and a collection of articles/essays by Rick Klaw (many of which had appeared on his "Geeks with Books" column at SF Site) ruminating on everything from book-selling & signings, comics & science fiction and censorship: Geek Confidential: Echoes from the 21st Century.

In 2005, alongside Philip Jose Farmer commentator Win Scott Eckert's guide to the Wold Newton Universe, the Locus award-nominated Myths for the Modern Age (whose contributors include Philip Jose Farmer and Jess Nevins, among others), Chris Roberson edited the first volume in a projected annual series of Adventure anthologies, comprising "original fiction in the spirit of early twentieth-century pulp fiction magazines" across the genres, featuring contributions from (among others) Lou Anders, Paul Di Filippo, Mark Finn, Michael Moorcock and Kim Newman.