Not sure exactly what kind of "sweet" you're after, but here are a few suggestions:
If you like a little "sweet spice", try a touch of Chinese 5-spice powder with a little salt & pepper. I find that a little dusting of it goes really well with gently-roasted or grilled chicken or pork. It contains Cinnamon and Star-Anise, which provide a natural sweetness. (I'm not sure how it would hold-up to high heat or smoking - if the flavors stand-up, it would be good with a kiss of smoke.)
If you like a combination of Sweet & Hot - try finding a good Jamaican-style jerk rub. They often contain a fairly complex mix of spices with a sweetness and some heat.
I've also seen some basic spice rubs used in conjunction with a sweet marinade - such as root beer or Dr. Pepper soda, but have not tried that (yet) myself. However, these seem to be oriented more towards pork than chix