Generally, cloud computing services fall into these three broad categories:
IaaS is the most basic level of cloud-based solutions, which refers to renting an IT infrastructure as a fully outsourced service. In this category, the cloud provider lets you rent servers, VMs, storage, network and operating systems on a pay-as-you-go basis.
Amazon EC2 and S3, Google Compute Engine, Windows Azure.
PaaS is the cloud solution where, apart from providing an infrastructure, cloud providers also issue an on-demand computing environment to develop, test, run and collaborate with components such as web servers, database management systems, and software development kits (SDKs) for various programming languages.
AWS Elastic Beanstalk, Heroku, Windows Azure, Force.com, Google App Engine.
SaaS providers offer fully functional web-based application softwares tailored to a variety of business needs such as project tracking, web conferencing, marketing automation or business analytics.
Google Apps, Microsoft Office 365, Gmail, Yahoo and Facebook.
These three different types of cloud computing services also offer different amounts of convenience and different amounts of control to the user. In that regard, they stack up as such: