Q:

Where to find/buy full list of updated ISP IP ranges?

I need to assign IPs of a huge daily visitor IPs to the ISP they come from. So I thought of buying the list of IP addresses corresponding to ISPs.
Now so far I have only found:
ip2country
But I am not sure how legit they are and dont want to get a database full of wrong data!

A:

One of the primary providers of IP information is MaxMind.  
http://www.maxmind.com/
While they have many products, this one is their ISP database:
http://www.maxmind.com/app/isp
They have a number of interface methods as well (e.g. c library, apache module, php modules).
The sites I've worked with have mainly used it for GeoIP purposes tied into web analytics.

