Tourist and Business visas are not required for citizens of the United States for a stay up to 90 days. However, your passport must have at least one blank visa page and be valid for six months. If your passport is expiring or you need to have additional pages added you can view the requirements here.
Fast Passports & Visas always recommends checking with your airline as requirements may change without notice.
Singapore requires that citizens of most countries obtain a visa to enter.  The Consulate General of Singapore will determine the duration of stay upon receiving an application.
Business Travelers
Travelers visiting Singapore for the purpose of attending business meetings/discussions/negotiations.
Social Visit 
Travelers visiting Singapore for the purpose of visiting friends, relatives, or tourism.