Seems like the longest single word domain name is named after a welsh town – http://llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch.com/
This is a 58 letter domain!
But this is not the longest place name in the world. That goes to one place in Thailand – 163 characters in length (I don’t want to write it here.. it will mess up my CSS 
What company is the best Domain Registrar? i’ve heard that Godaddy and Moniker are the best.”.*
GoDaddy will give you good rates.. but as far as the Best registrar rating is concerned, I am not sure which one takes the title. There are so many of them now. I have used Network Solutions, GoDaddy, Register.com and Dreamhost. I wasn’t a big fan of Network Solutions and Register.com though, because of their prices and complexity of user interface for managing the domains and domain services.
i always buy domain names at Godaddy or Moniker because they are the most reliable registrars:*.