At TGS 2010, Sega revealed  Phantasy Star Online 2, which is scheduled for release in 2011, ten years after the original PSO came out on the Dreamcast.  The new PSO2 is going to be released on the PC, and is currently assumed to be Japan-only.  This will be the second PC PSO release after 2005's PSO: Blue Burst, and the first new PSO title after PS0 on the DS.  Not many details are available right now. 
 
There is a trailer at SegaBits, which mostly shows clips from the Phantasy Star games over the last decade (PSO, PSU, PSP, PS0).  PSO-World have some information translated and will probably have more as it is available.