I used a Spinnaker Monk Tarp for this past weekend's trip.
It can pitch many ways. I usually just pitch it in a high a-frame when hot and if the wind starts blowing rain under it, I get up and drop the pitch to the ground and stake one end down so that only one side is open.
I use mine with an SMD Meteor bivy for bug protection, some spray protection and ground cloth. The combination can keep me dry in bad conditions.
If I didn't use the Meteor, I'd opt for something larger like 9X9 or 8×10.
Make sure you are comfortable and confident working with a small tarp before you buy it.