Kitchenaid stand mixer and attachments. Right now, we don't have any attachments but will be buying a few.
High quality cookie and baking sheets. I love airbake cookie sheets and am going to invest in a few true half sheet pans.
Knife set and block. Our first knife set was from Wal-Mart, and buying a cheap Cuisinart set was a major upgrade. Those wore out, so I'll be upgrading once more.
Cutting boards. I love the color coded cutting boards. They're great for preventing cross-contamination.
What are you kitchen must-haves?