The EFF's Fred Von Lohmann provides this list of how many subpoenas have been delivered to which ISPs. Data is based on subpoenas that are currently available electronically from Washington, DC District Court, which Fred says is a few weeks behind in posting them, but you get the idea of the first 150 or so:
1 Bentley College
1 DePaul University
1 Loyola University Chicago
1 Massachusetts Institute of Technology
1 Pacific Bell Internet
2 Adelphia Communications Corporation
2 Boston College
2 Earthlink, Inc.
4 Verizon Internet Services, Inc.
14 RCN Corporation
15 Time Warner Cable
21 Charter Communications
29 Comcast Cable Communications, Inc.
31 SBC
