Roofs and Crowns
I've decided that two of the most expensive and least satisfying things to spend money on are new roofs and dental crowns. You can't really open your mouth and say, "Hey, look at this new porcelain beauty on that back molar!" And you can point out your roof, but if it's like mine, it looks just the same as the old roof. In fact, I can't even see a difference except for the lack of the hole that the raccoons made. No one seems the least bit interested in the new roof and who can blame them.
No, roofs and dental crowns are extraordinarily expensive and while both are vital (nothing like a tooth ache or a leaking ceiling to ruin your day), they are completely invisible monetary sinkholes.
Just in case you are wondering, I have both.