I've been adding garlic, black pepper, paprika, bay, cumin & fresh dill to mine lately.
Have seen some recipes online calling for allspice, thyme, marjoram and/or caraway, but I haven't tried adding those spices yet.
Also, what kind of vinegar do you like to use? I've been using wine vinegar or white balsamic lately (even if it isn't authentic, it tastes pretty good!)
What do you like to add to your borscht?