+1 on Sans Digital's enclosures. Although, if you're looking for something with transfer speeds of at least 600 MB/s, I'd recommend one of their SAS solutions. The TowerRAID TR8X+P is an eight-drive enclosure with mini-SAS connectivity. According to Sans Digital, you should see average speeds of around 700 MB/s in RAID 0.
The issue with eSATA is that no matter how many drives are in the array, you'll still be limited by the 265 MB/s maximum transfer rate of the actual eSATA interface.