I really like Shan Gao's approach , summed up here :
http://philsci-archive.pitt.edu/14836/1/feels%20v999.pdf (which builds on his previous work, as well as David Z Albert's et al. 's work.)
(An interesting contribution is also that of Evan Harris Walker. It is much less comprehensive than Shan Gao's & does not amount to a full-fledged theory of consciousness, but it convincingly describes some relevant processes within the brain.)