I've been in business over 21 years, so I can't even find a lot of the books and resources I used in the early days but here are some that I do remember. The top two had a profound impact.
Taxpayer's Comprehensive Guide to LLCs and S-corps
This book easily saved me six-figures on taxes over multiple years. It's the best book on S-corps I've found and is written by tax accountants and updated frequently as tax laws change. It's worth it's weight in gold.
Financial Intelligence for Entrepreneurs
Great for entrepreneurs who don't have a finance background or slept through college accounting classes (or just didn't go to college). This book explains business financial reports (profit & loss/income statement, balance sheet, cash flow statement) in a way that you can understand and more importantly, teaches you how to use financial reports to determine the financial health of your business, forecast trends, and foresee problems that may arise.
Deduct It!: Lower Your Small Business Taxes
This is a good book that simply explains small business deductions, expenses, and how to use them to lower your overall tax burden. If you're new to business, there are probably some things you're not deducting that could save you money, or you may be taking deductions that are not allowed and putting yourself at risk of an audit. Understanding what is and is not deductible is important.
Accounting All in One for Dummies
Just a general all-in-one book on small business accounting. I use it more as a reference, I don't want to learn accounting I just want to know enough about my accounting and books to make sure I'm not making mistakes and to understand what my CPA is saying.
https://www.amazon.com/Financial-Intelligence-Entrepreneurs-Really-Numbers-ebook/dp/B005DI8XV2
Always helpful knowing a bit about finance. The above is an easy intro. Not sure the difference between the original book which I have and the "for entrepreneurs" version though that was just the first to come up on Amazon.