I go by the Alton Brown rule - never buy something that you use only for one task, unless that task is nearly daily for you.
I knew there was a reason I liked you mandalinn!
I am a big AB fan and I subscribe completely to his idea that everything in your kitchen should multitask.
These are a couple of larger ticket things, but they're invaluable to me:
I bake a lot of things and for my husband and I (or just for me) it makes more sense to bake in a toaster oven, than to heat up the whole big oven. Mine is just big enough that I can roast a chicken in it, or cook a small frozen pizza for DH, or put the square pyrex baking pan in it (for baked rice). I bake fish in it at least 2x a week and roast veggies at least that often as well. I have used my big oven maybe 5 times all year.
George Foreman Grill
I buy boneless skinless chicken breasts at Sam's club, marinade them in light italian dressing or a homemade teryaki mix and then grill 5 or 6 of them at a time (in 2 batches). They're great hot off the grill for dinner and I refrigerate or freeze the rest to use in salads, pasta, rice, etc. for lunches and dinners on nights I don't want to cook. It's also great for pork chops, hamburger patties when it's too cold to grill out, and a handful of other things. I also have used the grill to make homemade panini type sandwiches with whole grain pita and lean turkey or ham. Yummy.
I'll also second the microplane grater and a good knife. I also like and use the Global knives. I have a friend's house where I actually refused to cook unless she bought better knives - bad knives aren't only annoying, they're actively dangerous!