A horse. Even though I have no time or money for one. I do really LIKE horses, and I used to ride, so it's not completely unreasonable...but yeah.
A giant fishtank. I really love the look of a well-put-together and well-maintained fishtank. But I know I don't really have the time or the skills to put it together, the novelty would wear off, I'm sure. And I don't know where I would put it.
A new car. And I mean new-new, not new-to-me-new. Even though my current one is perfectly fine. And I also don't have the money.
A Nook/Kindle. I nearly bought one online on Black Friday, but stopped myself. I know I either won't use it enough for it to be worth it, or I'll use it way too much and spend way too much money on books. Willpower.
ETA: And chickens! Ever since one of our family friends started bringing us farm fresh eggs, I have wanted chickens. The eggs are SO MUCH BETTER. And of course, I could always buy farmers market eggs, but I really have this weird desire to have the chickens too.