Serial ATA is the new standard replacing the old IDE, or parallel ATA. Its a much faster interface then IDE, starting at 150mbs and should see as high as 600mbs data transfer speed. IDE has max'd at 133, and SCSI is 166mbs. Serial hasn't been on the market except maybe 6 months and is coming on very strong.
Serial ATA offers you the ability to have faster drives than ide without the pain of scsi. They have some crazy seek time sata drives out that are almost ( 5.xms ) twice as fast as standard 9.0ms IDE drives.