What top-level domains do you register?
aneesh: Don't go overboard.  For example, neither facebook.org nor facebook.net redirects to facebook.com.  And you don't even have to own the .com.  37Signals doesn't own the .com for any of Backpack, Basecamp, Campfire or Highrise.  Get the .com, and then go worry about making it good, instead of worrying about what other tld you need.