My favorite food/condimment pairing is malt vinegar on thick cut fries. My second favorite is probably either spiced honey mustard on thin, crispy sweet potato fries or buffalo sauce on wings.
I like most condiments that I've tried for certain things. I can find a use for almost any barbecue sauce. A1 is good on a burger, especially if it has mushrooms on it too. Worcestershire sauce is good added to a lot of things. Ketchup is good on a cheese burger or hasbrowns (although egg yolk is my favorite hashbrown "condiment"). Mustard is good on hotdogs, brats, pastrami, ham, bologna and various lunch meats. A little horsradish mixed with mayo is great on a medium-rare roast beef sandwich. I love rice with just a little soy sauce and sriracha mixed in. Maybe some chives or green onion too. I like sour cream and guacamole on a lot of different things. Plain yogurt works pretty well as a sour cream replacement. I like italian dressings, especially homade, on various sandwiches/subs. I love french and catalina dressing, especially jazzed up with a little lime and chili sauce, on veggies and veggie sandwiches.
I think whip cream, butterscotch sauce and chocolate syrup are great condiments for ice cream, cakes and cookies. And caramel is a great condiment for apples.
There are a lot of the creamy salad dressings that I'm real picky about. Like, ranch is meh, unless it's home made or made from the Hidden Valley brand packets and then I really like it. A lot of the standard shelf blue cheese dressings (kraft, wishbone, etc) are gross. I like the T. Marzzeti's brand that comes in a jar but not the one that comes in a bottle.
Oh, I hate Thousand Island dressing. Gross gross gross! And a lot of pre-made tartar sauces are gross too.