Hands down, BBQ sauce. I have ten in my fridge now and use them all for different things. I’m always trying new ones and creating dishes FOR certain sauces.
I’ve very recently experienced a new favorite. The cafe where I work has a small garden. Some vegetable, but a lot of herbs and such. Among the veggies are jalapeno peppers. The boss made a mistake, thought it was a bell pepper plant.
One co-worker, who likes spicly food, ground out of the garden fresh jalapenos as fine as he could, and added the pulp to ranch dressing. Just enough to make it hot, but you can taste the food. Oh my, the difference using fresh peppers makes. Using canned would not be near as good. We now have it for a dip for Tuesday’s chicken tenders. Really nummy.
I came in to say Hellmann’s, and tapenade was in the running as well. Now you have clued me in to the best of both worlds.
That sounds really good, even though I’m not the biggest fan of ranch.
Mustard. Not by much, I like a lot of other condiments, but mustard is the most versatile and available of the condiments I use.
Hi…my name is Gary, and I like ketchup.
Tabasco sauce.
Za‘tar زعتر. I put it on ḥummuṣ bi-ṭaḥīnah حمّص بطحينة (literally ‘chickpeas with sesame paste’, known simply as “hummus”), both of which I make from scratch. I like to breakfast on homemade Italian bread dipped in olive oil (plus maybe some feta cheese and Kalamata olives), sprinkled with za‘tar. It isn’t easy to find the authentic Levantine herbs like Origanum syriacum, wild thymes, hyssop, etc., so I make it with regular thyme plus a little marjoram and oregano, while toasting and coarsely grinding the sesame with kosher salt.
*<Everyone answers in chorus> *
Hi, Gary!
Geez, am I ever a noob/amateur/small-town-hick in the condiment department. 
I am humbled and learn at your collective feet.
<Scribbles on shopping list to take to International Grocery Store>
I love many, but tapenade is fantastic, underrated, and underused.
Cleveland stadium mustard, and my mom’s green tomato relish (which I coincidentally just mentioned in another thread).
And I don’t think of olives as a condiment, but they’re a great ingredient in a whole lot of dishes.
I’m thinking it was Wendy’s that used to have jalapeno ranch dressing for their Baja salads. It was good enough to tip up and drink straight. 
I’ll bet the stuff with freshly ground peppers is even better.
For purposes of this thread, people can define condiment as loosely as they want.
I’ve been playing with new recipes lately and some of the favorites in this category are:
Carmelized Onion Jam
I was out of brown sugar the first time I made this so I subbed in Maple syrup. I’ve made it both ways now and I prefer the maple syrup version.
Great on bread or crackers as appetizers, on meat or cheese sandwiches, or when it’s approaching the end of it’s shelf life, with a spoon
I had a sandwich at a restaurant recently where they used a flavoured balsamic vinegar as a sandwich condiment and I’ve resolved to do that myself. I love balsamic both flavoured and standard versions and I’m looking forward to playing with combinations.
If you like sambal oelek and fish sauce, you need to try the chili oil from Brooklyn Wok Shop, or a similar one, just in case you haven’t already. It’s mainly ground red pepper, garlic, oil, and fish sauce.
I go through the jars so fast I’ve had to learn how to make it. It makes a great base for a pizza.
Honey! Can never get tired of it. You can call it bee vomit and I’d still find it appetizing.
I just remembered Secret Aardvark habanero hot sauce. If you like hot sauces, try this stuff. It’s amazing.
If I can have only one jar in the fridge, it would probably be salsa. I use it on many things and would hate to be without it.
But I also use, most days, mustard (prefer brown and Dijon); hot sauce (whatever’s on sale); chopped Vidalia-or-similar onion (I always have at least one on hand); chopped bell pepper, preferably a warm-colored one; and lots and lots of red wine vinegar. Use it a lot. I eat a lot of salad (lettuce, various cabbages) and veggies in general, and these condiments are wonderful for adding flavor and character. (Half-sour kosher pickles are another favorite, come to think of it.)
My very favorite thing, that I would love to have in the house every day, is tsukemono of all kinds, particularly Daikon radish (takuan). I know these can be made at home, but my present circumstances make that impractical, dang it.
Rooster sauce! On everything, dammit!
El Yucateco Green Habanero Sauce. This sauce is hot, obviously, but has a wonderful fresh flavor and is great on everything, baked salmon, herbed potatoes, egg dishes, all meats, all seafood, I shake it into a bag of potato chips and enjoy it with a couple cold beers, a few drops complete an Aioli like nothing else can. Hard to find but don’t be shy what doesn’t kill us makes us stronger!