I feel that a pork butt when properly cooked will stand on it's own with flavor and many people will not use a sauce with it. But then again, you will find that some people think the BBQ means sauce and really pour it on.
BlueDawg's Rub is a great start for seasoning. You can also try using an injection like Chris Lilly's to add flavor and help keep moisture within the cell structure of the meat. I add spice to the injection to boost the flavors.
I find it best to leave the sauces on the side and let the patron decide... I find many use no sauce at all, but people are individuals and have varied tastes..
Humphrey's DownEast Beast W/BBQ Guru