There are any number of remote services that you can use to perform functions, from payment gateways such as PayPal and Authorize.net, calculating geographical locations such as Google Earth and redline13's zip code calculations, to complex applications like the Salesforce CRM.
These services provide APIs to allow access to their SOAP and REST services. They can be quite simple to access, with the hardest part of using them being the decision of which API to select. This section will offer tips and tricks to show exactly how to use some of these services.
Perhaps the most important consideration with any of these services is security, and this includes the security of your user's data as well as your own access keys and passwords. Suggestions will be offered for the best ways to keep your data secure both on your server and while being passed over the Internet to the remote service.