We just switched over syrup brands at the coffee shop I work at and I can't get enough of the salted caramel, but only with steamed (soy) milk. The flavour with espresso just doesn't translate for me. I enjoy a flavoured latte, but I've become so accustomed to black coffee.
I've tried the pumpkin spice and I just don't get it. It's okay, but it's no gingerbread or maple in terms of an Autumn/Winter flavour.
hazelnut. it helps cover up the acrid acidity of office coffee.
I like Kahlua in my coffee, if I'm in the mood for something with a bit of alcohol but mainly I just buy coffee roasts that I can drink without having to add much of anything. Raw or coarse sugar is just fine.