For me, it's malt vinegar on fries, if I put anything on fries at all.
No ketchup. Never ketchup. Ketchup is the enemy of all things good.
Mayonnaise is the worst unless you make your own - and even then it's questionable (at best).
As far as mustards go, I love the classic Gulden's Spicy Brown, as well as Grey Poupon, horseradish mustards, and various Inglehoffer's coarse mustards. I can't do the basic yellow mustard from French's or whatever unless it's the only thing around.
As Chef said, salt and pepper are the ultimate condiments, and too often underused.
My go-to hot sauce is Frank's original, but I have some local favorites as well.