Normally, I like to keep it simple with duck: Salt & Pepper, sage & a little dried Rosemary. The Sage & rosemary work really well with the richness of duck.
I bet scooter's suggestion of Jalapeno salt (Jalalujah) would work well as a combo with a little sage.
Every duck I have smoked in the past I liked beast with fresh cracked sea salt and fresh cracked pepper rubbed into it with a bit of olive oil rubbed on the skin before the s&p