I’d personally say the "Rich Dad Poor Dad" series by Robert Kiyosaki. I respect that it’s super popular and has helped a lot of people, but I find a lot of the advice pretty questionable. The whole “two dads” analogy also makes the book feel longer than it needs to be. Even for beginners, I think there are better options - like "I Will Teach You to Be Rich" by Ramit Sethi.

I feel Dave Ramsey should also be mentioned. I know he’s helped many people get out of debt, but a lot of his online advice seems a bit extreme.