I smoke everything I can.
As mentioned above, prime rib is great, so is tr tip, really anything you have grilled on your BBQ or make on your stove/oven.
I like to do multiple types of fish, I really like lobster and shrimp, lamb, chicken and anything from a cow or pig.
Smoked cheese, and smoked mac and cheese.
Also don't be afraid to smoke berries. You can use them for jam, glazes, sauces etc etc and it is phenomenal!