we are using sharepoint 2010. We have a scenario where we need to crawl external non-Sharepoint websites to show up in search results after crawling the external sites. What are the ways to configure the external sites so that that site data could be avalable in search results?
You'll want to use federated search. When set up, if people search for widgets, it will look against your internal content and display results for widgets as weill as pull in information from Google or Bing about widgets in a seperate result set typically set on the right hand side of the search results screen.
Just configure a content source that crawls the external web site (a Web Site content source). I am not clear on what you mean by "Site Data". If you mean pages and documents that are linked to those pages, SharePoint does that out of the box.
In SharePoint 2013 you can crawl these site anonymously, which can be a consideration for some crawl scenarios.