I found this article on Network World that lists the top 10 ISPs at the end of 2000 (based on market share). The article is here:
http://www.nwfusion.com/newsletters/isp/2001/00846039.html

And here is their list:

1. WorldCom 27.9%
2. AT&T 10%
3. Sprint 6.5%
4. Genuity 6.3%
5. PSINet 4.1%
6. Cable & Wireless 3.5%
7. XO Communications 2.8%
8. Verio 2.6%
9. Qwest 1.5%
10. Global Crossing 1.3%

Obviously a lot probably changed over the last year but I bet the numbers are still pretty close. What I find interesting is that, even if 70% of PSINet's customers left (and I don't think it was that high) after they went into chapter 11, Cogent would still be a top 10 ISP after the merger is complete.

I am looking high and low for a more recent one. I think Boardwatch has it. I am pretty sure XO and Qwest were above them now. Maybe even CW. Also, this came from year end 2000

"Probe breaks down ISP market share based on year-end 2000 revenue"

2001 was not a good year for PSINet

Originally posted by UmBillyCord
I am looking high and low for a more recent one. I think Boardwatch has it. I am pretty sure XO and Qwest were above them now. Maybe even CW. Also, this came from year end 2000

"Probe breaks down ISP market share based on year-end 2000 revenue"

2001 was not a good year for PSINet

I don't think you will find a more recent one. The ones from boardwatch and other places, are still using Year 2000 Revenues. A list using year 2001 revenue probably won't be ready until May of this year.

And remeber, this is just based on market share (number of customers). There are other ways of measuring, that would produce different results (that's why I included the link, so you could get information about the methodology).

As to PSINet, it sure wasn't a good year for them, but I am fairly certain from talking to people I work there, that they did not lose more than 50% of their customers (obviously that is bad), which would still leave them in the top 10.