A Little Hatred (The Age of Madness Book 1) by Joe Abercrombie is $3.99 today. https://www.amazon.com/dp/B07MJ656W9. This is a great book, Abercrombie's best IMO. The sequel is coming out in September so not long to wait for it. It's a complex story with a lot happening and there are many of the characters we know and even more new ones. Set earlier than the original First Law Trilogy, it tells how that world came into being and how the characters became who they are. It's a more detailed book and is a true can't-put-down story with lots of Abercrombie action. But character development drives this story and what characters they are. Also Abercrombie's books are rarely offered with discounts so take advantage of it if you are a fan of the First Law World.
The Way of Shadows (Night Angel Book 1) is $2.99 https://www.amazon.com/dp/B001E0V112 There's been some good comments about this great series in the main thread lately and I liked it better than the Lightbringer series which is also great.
Fated, the first book in Benedict Jacka's Alex Verus Urban Fantasy series, is on sale today for $1.99. I haven't read them (though I just bought this one) but have heard good things. Sounds kind of like Dresden set in London.
Sixteen Ways to Defend a Walled City by K.J. Parker is available for $2.99 today. I've never read any book by Parker, but he's supposed to be quite good.
The Calculating Stars and The Fated Sky, the first two books in Mary Robinette Kowal's Lady Astronaut series, are both on sale for $2.99 each. The books are pretty highly acclaimed, with the first book winning the Nebula, Locus and Hugo awards trifecta for Best Novel.