In order to be successful, businesses are going to have to form relationships (vendors, customers, partners, etc.) and to be protected when they do so. Many of those relationships should be formalized in a contract; it's one of the easiest ways to minimize your business risk.
Here are a few contracts that businesses should have in place:
Founders Agreements
These are important as they cover ownership, responsibilities, decision-making processes and what happens when something goes wrong between founders
IP Assignments
It's common for founders to transfer or assign relevant intellectual property to the company. It's what helps get the company off the ground.
NDA
Non Disclosure Agreements create an obligation to privacy and are one of the most effective ways to make sure your trade secrets and other confidential information stay secrets.
Commercial Lease
Many companies need space to run their business, make sure you have a written agreement that details everybody's responsibilities.
Employee Agreements/Independent Contractor Agreements
In order to grow you're probably going to need help, make sure that employees or independent contractors have agreements with terms detailing the relationship.
Service Agreements - make sure they include a Statement of Work when necessary
Just about every business uses a service provider and many businesses provide services. There should be one for your vendors and clients if you're a service provider. They usually contain a statement of work that details the nature of the services or deliverables.
Website Terms of Use and Privacy Policy
Almost every business has a website these days, and many of them are collecting information from customers or clients. Privacy is a necessity, so letting your clients and customers know what you're doing with their personal information is essential. These terms and policies may differ based on your business but essentially they should all address the products and services your offer, any limitations on your offers and any guarantees that are applicable (you have taken some security measures to protect personal information).