Having your own personal Internet Domain Name is the first step towards building an identity and setting up your own corner of the Web. A domain costs money, but a cheap one costs as much as a telephone number.
Because the domain serves as a foundation to your online identity, it should be chosen carefully and considered permanent as much as possible. There are a few tools like CunningBot that can help you choose your domain name and others like Instant Domain Search that can quickly search under which TLDs that name is available. There are also tools like Namechk that probe if common platforms and social networks will have that name as an available handle/username, which can be nice for consistency.