We'll know this for sure within a few days (hours?) but I thought I would take a stab at what lenses they'll announce.
Most likely
35mm 1.4 II - priced somewhere between $1700-$2100
200-400/1.4x - priced at $10k
Possibilities
TS-E 90 II - magnification near .5x, similar updates to other TS lenses, priced at $2100
TS-E 45 II - similar updates to other TS lenses, priced at $2100
400/5.6 II - much sharper. Has new gen IS. Priced at $2300.
300/4 II - much sharper, takes extenders better. Has new gen IS. Priced at $2300
Unlikely
100-400 II - no more push/pull, much sharper and faster. Priced at $3000.
135/2 II - Priced at $1900.
MP-E 65 II - Significantly better optics, maybe increased magnification. Priced at $2300.
Not happening
14-24 - Maybe an "in development" announcement, which means 2014