Cross-Site Scripting attack

[Deepa Khetan]

Hi,
 I am working for the Security of my site. Read about Cross-Site-Scripting
attacks being most common. Can anyone help me regarding what can be the best
freeware tool to test a CSS vulnerability of my site. Also, any suggestions
on how CSS attack can be avoided? We are using Struts framework.
 Any information/suggestion is most welcome.
 Deepa