You can choose an alternative Domain Name, or if you feel that you have legal rights to a particular domain you could initiate a Uniform Domain Name Dispute Resolution Policy ('UDRP') dispute by submitting a complaint to one of the ICANN approved dispute resolution service providers listed at
http://www.icann.org/udrp/approved-providers.htm, that states:
1. The Domain Name you are complaining about is identical or confusingly similar to a trademark or service mark in which you have rights; and
2. The Registrant of the Domain Name you are complaining about has no rights or legitimate interests in respect of that Domain Name; and
3. The Registrant has registered and is using the Domain Name you are complaining about in bad faith. In addition, your complaint must conform to the Rules for Uniform Domain Name Dispute Resolution Policy, which are available at
http://www.icann.org/udrp/udrp-rules-24oct99.htm, as well as the selected administrative-dispute-resolution service provider's supplemental rules.
For example, you believe that you have legal rights to the Domain Name 'tonismith.com' but it is has already been registered by someone. The UDRP will inform you how to pursue your claim.