Peri peri or a lemon butter one or so for me. Or Tomato salsa done just right. White wine sauce with cream, garlic, mushrooms etc can be so absolutely amazing too.
So many damn good sauces out there tbh! I love Nando's Peri Peri especially or Cholula's for example:
Sauces with lemon or coriander or especially both are heavenly too!
If Hummus counts too, that is AMAZING when done right too! Especially lemon and coriander/cilantro again haha.
Proper Italian tomato sauce is fantastic too. A while ago I ate at a traditional Greek restaraunt, lamb mince with rice wrapped in vine leaves and topped with a tomato sauce with a bit of a citrus/lemony tang to it and such, it was INCREDIBLE! Also their garlic sauce mushrooms too! Best ones I've ever had!