Mayo's my favorite.

Recently I've started making a "shredded tomato dressing" for my salad. I buy some grape tomatoes, run them through my hand-crank salsa chopper (like a food processor) for a very coarse chop, to sliver up the tomatoes, and then stir in a bunch of mayo. The juice makes the resulting sauce the right consistency to pour over salad from one of those lettuce variety bags in the produce aisle.

For sandwiches, mayo, dijon mustard, and that fine Inglehoffer horseradish. The hotter Beaver brand horseradish is also good. (Inglehoffer is actually Beaver's high-end brand.)

For hot dogs, brown mustard. Gulden's is good, or I'll just use the store brand. But never yellow. Yellow's ok for the yolk mixture of deviled eggs, along with a bit of Miracle Slop.

For burgers, Miracle Slop and a dab of brown mustard and a dab of catsup. (And lots of blue cheese.)

For fish, my mood changes from tartar sauce to lemon juice to malt vinegar.

For sub sandwiches, Thousand Island dressing.