Geoip lookup

What's the best way to find the networks in a country? I was thinking of writing some perl with Net::Whois::ARIN or some such module and loop through the block. But I think I'll have to be smarter than just a simple loop not to get blocked and I figure I'm not the first to want to do this. I've noticed some paid databases out there. They don't cost much but are they even worth what they charge? Ie, countryipblocks.net doesn't list quite a few addresses from a country I've looked at blocking. Isn't this information free from the different *NICs anyway? This is probably two questions: a program that smartly looks for country's blocks in a block and are GeoIP services worth anything?