Saba Rock is a tiny little island just off of Virgin Gorda. You can walk around the circumference of the island in easily less than five minutes. Despite it's size it sports a nice restaurant and bar and a gift shop as well as a small resort. There is a small but impressive outdoor aquarium next to the bar.
The mooring fee (around $25) at Saba Rock includes a fill of your boats fresh water tank and two bags of ice.