Mario Batali was just on the Rachael Ray Show, and an audience member stood up to ask a question: What would Mario say were the top five dried spices to always have in your pantry?
Well, the first thing Mario said, I've heard him say before: "Go home and throw away all of your spices." Then he went on to say that he knows you have some curry spice that you used to make Tikka Masala in the 80s and it tastes like wood chips now. Fair enough. I know I keep my spices for way too long sometimes!
The top five spices Batali recommends are: basil, oregano, coriander, mustard seeds, and for desserts cinnamon and nutmeg ("I get two sweet spices," Batali said, always the bad boy.) See his full answer here: http://www.rachaelrayshow.com/show/segments/view/audience-q-mario-batali/ 
I'm not sure what my top five would be. I guess it depends. I recently had a bad experience with some Mexican oregano. It's SO much stronger regular oregano, that I made a mistake with a rub for a pork shoulder to be slow cooked in a crock pot. My pulled pork was still good, (how could it be bad, really?), but the oregano overpowered it, big time.
I know I use a lot of cumin, since Mexican food is probably my favorite cuisine ever, and a Monterey Steak seasoning blend has been getting a lot of use on boneless, skinless chicken breasts and zucchini slices for the grill...
What would you say are the most-used spices in your spice rack?