Scott's Cheap Flights. No affiliation. I probably don't travel enough to justify paying, and when I can travel I just buy the dates available, but if you have lots of spare time, they do a great job of curating low-cost tickets. I especially like that they mention things like "no bag fee" and "nonstop" — not just some random aggregator, but actually handpicked and digested.

https://scottscheapflights.com/