Rapid growth of published Web services makes their discovery more and more difficult. Many approaches are proposed to solve this discovery issue. Most of them are interested only in Web service's description itself and neglect the user-centric aspect of the discovery process. User's involvement may be seen as contributing information, after using or testing a service, which marks the personal opinion on service's functionality, quality or invocation cost. This kind of contribution is perceived as a participative aspect inside the Web 2.0 environment and can enhance the Web service discovery process. We illustrate in this research work, a collaborative tagging-based environment for Web service discovery, allowing users to tag or annotate a Web service using keyword or free-text. Our system proposes consequently two types of query to search tagged Web services: keyword-based and free-text. We put in place an advanced mode in the discovery by keyword which offers different ways to combine keywords together inside a query to make it more flexible and accurate. In both types of look-up (by keyword and by free-text), synonym relation between terms is processed in order to improve the similarity computing between a query and the tagged web services. The Web services found after a discovery process are ranked according to their tags' weight, in the case of discovery by keywords.