Beef tenderloin is widely regarded as the most tender cut of beef, and it's certainly the most expensive. It's a portion of the ever-popular T-bone or porterhouse steak, and the upscale filet mignon comes from it as well.
 
Key insider tips: Cook a tenderloin quickly over high heat (like on the grill) so that the exterior becomes nicely browned while leaving the interior juicy and medium-rare. You can also sear it in a smoking hot skillet on the stovetop, then finish it in a 450 F oven