Here's another recipe I've grown fond of.  Mainly because it's simple and it's all in the grilling, not so much the preparation.

Get a slap of loin.  
Brush olive oil over it
Now on one side, sprinkle:
Cracked pepper
Sea Salt(the large grain stuff)
Onion powder
garlic salt

That's pretty much it.  You can be liberal with this stuff.  The loin is a thick piece of meat.

Now, take it to the prepared grill.  Quickly sear around the entire loin over direct heat.  

Once that is accomplished, move the loin over to the side and cook with indirect heat for about 30-45minutes or until it's done.  Remove from heat and wrap in foil and let it stand for about 10-15minutes.  Cut and serve.