Roger Pearse has linked to the first 14 volumes, with the 15th volume also available. Images of the papyri for vols 41-68 are now online, and it also includes an index to vols 1-68 (this means there is a short description of each papyri--very useful).
Papyri.info is a searchable papyri database that is not limited to just the P.Oxy. group.
A list of OT and NT P.Oxy. documents.
A closing word from A. T. Robertson from his book The Minister and His Greek New Testament:
But enough has been said to show how rich the papyri are for the student of the Greek new Testament. The best linguistic commentary on the Greek New Testament is the papyri of the first century A.D. and the Septuagint. It is now possible for any eager student to have both these privileges without having to sell his coat to get them. (last paragraph of Chapter II)
Sell your coat, nothing! With all of this available online, you won't even have to put it on.