We've spoken a lot about Restlets in previous posts... It was without counting on another RESTFul framework which begins to be widespread too, ie Jersey.
As said on their web site :
"Jersey is the open source (under dual CDDL+GPL license), production quality, JAX-RS (JSR 311) Reference Implementation for building RESTful Web services. But, it is also more than the Reference Implementation. Jersey provides an API so that developers may extend Jersey to suite their needs. The governance policy is the same as the GlassFish project. "
As I've currently an opened post -), I give you another link towards the Enunciate project which is also interesting for building web services, RESTful or not (rest, soap or RPC).