The United Explorer Card has an offer to earn up to 70,000 bonus miles: 60,000 after you spend $3,000 on purchases in the first 3 months and an additional 10,000 after you spend $6,000 in the first 6 months. That’s still just an average of $1000 a month, so easily doable for most readers.
This is a nice improvement over most of the elevated offers there have been for this card. And it comes with a $0 the first year then $95 annual fee so you aren’t even paying that first year fee in exchange for the additional miles.