Wowbagger's post about finding a pack of couscous eight years past its best-by date reminded me about the jar of asafoetida I finished in a veggie curry the other night.
Best before the end of December 2002.
Yes, I know, some people say you should replace your ground spices on a yearly basis, but I go with a smell test - if the aroma hasn't faded, why chuck it out? Put it like this, asafoetida used to be sold double-packed in miniature plastic tubs with screw-on lids inside the jar, because it's pretty pungent stuff (IIRC it's used as a garlic substitute in some Indian recipes) and it was still minging quite strongly years after its nominal best-by date.
Looks like the oldest thing in the kitchen cupboards is the tin of Colman's mustard powder, which was best before the end of March 2004. Not sure about the jar of Szechuan peppercorns, but they might be of a similar vintage...