Since you are using SharePoint 2010, you are in luck!
You have 4 options:
Use the Client Object Model provide by SharePoint Foundation 2010 CSOM
Use the REST API provided by SPF 2010 CSOM
This provides a subset of Client Object Model functionality, but this will do what you want.
Create a custom WCF RESTful Service, hosted in the SPF 2010 server.
This will require more work. It is more complex. But, again it will do what you want.
Use the ASP.NET Web Services
These are legacy asmx services that were also available in SharePoint 2007. MS recommendation is that use only these services for backward compatibility. In other words, avoid using them in new solutions.
Based on your question, I will choose option #1. If that does not meet your needs choose option #2, then #3.
The MS Developing SharePoint 2010 Applications Guidance provides good documentation on this topic as well. More specifically, check out the section titled: "Using the REST Interface"