The Jesus Myth theory stands on 3 legs:
(i) Jesus is not known in early and authentic non-Christian texts;
(ii) Paul in authentic writings does not know of a historical Jesus, but only a spiritual figure known from revelation and cryptic interpretation of scripture;
(iii) the Gospels are not history but allegory and pastiche drawing on the Old Testament.
The biggest hitters in this area at the moment are Earl Doherty, Richard Carrier and Robert M. Price.
Edit: as of June 2014, Richard Carrier’s new book, the first ever peer-reviewed, university press-published argument for a mythical Jesus, is the definitive analysis of the whole issue, and to my mind proves the theory. Short essay summarising his case.
The Jesus Seminar was a major academic project to try to identify authentic Jesus traditions.
The Jesus Myth theory
Second edition of Earl's book (a simply amazing book!)
A clever graph showing how late the narrative details of the Jesus traditions developed in the sources excluding the (fictive and little known!) Gospels
Vridar - the best amateur blog on NT reliability and Mythicism topics
My favourite series of articles proving the reattribution of Ignatius' letters to Peregrinus
A curious and enthralling series of articles arguing that the original author of the Pauline epistles was the arch-heretic, Simon Magus.
Robert Price’s book on the historical Paul, again theorised to be Simon Magus.