All business income tax returns are actually just financial statements that have been modified to a format required by the IRS.  The income tax returns required by the IRS are as follows:

Corporation: Form 1120
Subchapter S Corporation: Form 1120S
Partnership: Form 1065
Sole Proprietorship: Form 1040, Schedule C
Limited Liability Company (LLC): may file any of the above

This IRS article provides more detail about which types of businesses file which returns.

The IRS allows businesses to choose some accounting methods used in tax return calculations, such as cash whether to use cash or accrual accounting.  Inventory valuation methods used in tax returns may also differ from business to business based upon the circumstances.  This IRS article describes when various methods may be used.

Other items, such as depreciation and amortization schedules, are often strictly dictated by the IRS.

If you own a business, your banker and your investors will likely require you to send them copies of your tax returns.  This allows them to analyze your financial situation using a statement on which you are not likely to overestimate your income.