[wibblenut]

Fastest way is to check whether it exists in the nightly zone file, and then a DNS lookup, and whois query.

[mseebach]

What is the nightly zone file?

[aquarin]

It is zone file from the last night (or day). It requires free account from Verisign for .COM and .NET. I used such account for a while.

edit: "Zone file" is the file containing the records of all registered domains in a zone (.com or .net). Last time I checked it was something 80M records for .com