Doncha know that
any kitchenware you buy will become your new best friend?
Something you think you have little use for suddenly becomes one of your most used items, and you wonder how you ever did without.
That said, however, and depending on how big the gift certificate is, I would go with one of two items:
1. Stock pot. My first option would be a large stainless pot with built-in strainer and steamer. This makes it an incredible usefull, multi-purpose pot. How big? Depends on the size of your family and your cooking style. But in any case, go up at least one size from the one you think you'll need.
2. Cast iron Dutch oven. At least what we call Dutch ovens today (and which LeCrueset is trying it's best to reclassify as "French" oven). For most people, porcelain coated is preferred.
A cast iron Dutch oven is arguably the single most flexible cookery item you can own. You can perform virtually any cooking technique in it, from sauteing to braising to deep frying; they clean up readily; the coated ones are pretty, etc.
Downside to the coated versions is, it goes without saying, price. They are unGodly expensive, expecially the LC versions.