Conservative, huh? They Republican? Get them an Obama mug. Just to see their reactions.
Seriously, though… You can’t go wrong with some good food. Wine, steak, chocolate, lobster, whatever. A pointsetta is good, too. Basically, get something that, if they don’t like it, it will be gone within a couple of months anyhow.
Alternatively, if you know (or your future spouse knows) what they’re lacking around the house, then buying that for them could be considered a lifesaver. Do they need/want a waffle maker? Go with that! Is their coffee machine broken?
Go with the practical items. That way you’re not contributing to the tackiness.