Today I needed to expose some REST functionality in the project, which leverages Sitefinity, via ASP.NET Web API.

Standard routing setup didn't work out for me. There is a little gotcha. You have to register routing after Sitefinity bootstraper is initialized:

 Bootstrapper.Initialized += new EventHandler<Telerik.Sitefinity.Data.ExecutedEventArgs>(this.AfterInit);
 private void AfterInit(object sender, ExecutedEventArgs args)
 {       
    if (args.CommandName == "Bootstrapped")
    {
       WebApiConfig.Register(GlobalConfiguration.Configuration); 
    }
 }