XMLspy is the best tool for xml editing. UI based editing of XSD and easy to use validation support is very~~~ good. Surprisingly, there are very few easy to use XML validation tools. Even microsoft provides with web form based UI for XML validation tool. (Very hard to manipulate; select file(xsd), select file(xml), and click upload button. and see the result. and start again.. again.. again..)
I even decided to make a new tool for XML validation cuz I was really disappointed by this lack of validation tools. But, Altova offer restricted version of XMLSPY for free. IMO, the free version per se is good.