In my recent experience, mopping the chicken while it smokes is important.
I did a couple whole chickens a few weeks back and forgot to mop them (went to a party and stayed too long). They were good, but dry.
I did a ton of chicken last weekend for my son's first birthday (plus seven racks of ribs and a bacon explosion). I kept the chicken moist with a mop sauce and it was awesome.
The dry rub I use is brown sugar, paprika, garlic powder, mustard powder, cayene, chili powder and maybe a touch of cumin (depending on my mood).
When I brined a turkey awhile back I threw typical turkey spices in the brine: rosemary, thyme, marjoram, not sure what else. I smoked this on the Weber and it came out very well.
If I was baking a chicken, I'd probably use similar spices on it. For smoking, I tend to go for the BBQ spices.