soapUI, is the world leading Open Source Functional Testing tool for Web Service Testing. It supports multiple protocols such as SOAP, REST, HTTP, JMS, AMF and JDBC. soapUI is from eviware, the Open Source TestWare Company.
Eclipse HTTP Client (HTTP4e) is an Eclipse plugin for making HTTP and RESTful calls. Build with user experience in mind, it simplifies the developer/QA job of testing Web Services, REST, JSON and HTTP. It is a useful tool for your daily job of HTTP header tampering and hacking.