Seems like VPNs / proxies could cause problems these days on forums where people like to have different "identities" / "aliases". With some motivation, I went and looked for ASNs which provides web/vps/dedicated hosting service (that are not ISPs) and saved their IPv4 prefixes in a "database".
http://check.getipaddr.net/check.php?ip=IPHERE Returns a value between 0-1 on how likely the given IP address is a proxy/VPN Returns negative values on error Error codes: -1 Invalid no input -2 Invalid IP address (ipv6 is not supported) -3 Unroutable address / private address -4 No dynamic server could be reached for your request
This information may not be 100% correct - Please PM me if there's a mistake. If you know some hosting IP that's not recognized as a proxy, PM me the IP and I'll look into it.
As mentioned in the title, it's a work in progress, hopefully it'll be more accurate as it develops.
Thanks to @Cakey for sharing apart of his list with me :)