As good as simple, plain mashed potatoes are, certain additions can make them even better. Here are some mashed potato variations - start with my mashed potato recipe and then add/substitute ingredients.
This garlicky soup is easy, quick, healthy, and delicious.
I'll never understand people who don't like garlic. It's an essential ingredient in so many cuisines, from Cajun to Italian to Thai. Sure, it makes your breath smell, but that's what toothpaste and mouthwash are for, so why deny yourself the wonderful flavors of garlic? Though not a vegetarian cookbook, Sarina Jacobson's Garlic includes plenty of excellent meat-free recipes, and many of the others can serve as inspiration for vegetarian adaptations.
These aren't much more work than regular mashed potatoes, but they have a lot more flavor.
Caesar salad often comes with anchovies, which offer a salty, "oceany" flavor. This Caesar dressing uses arame (a type of seaweed) to offer a similar kind of flavor to vegetarians.