Uri configurationServerUri = new Uri("http://your-server:8080/tfs");
TfsConfigurationServer configurationServer =         TfsConfigurationServerFactory.GetConfigurationServer(configurationServerUri);
ITeamProjectCollectionService tpcService = configurationServer.GetService<ITeamProjectCollectionService>();
foreach (TeamProjectCollection tpc in tpcService.GetCollections())
{
   List.add(tpc .name);
}