It may not be the greatest named application out there but SQL Sentry Plan Explorer is a free, lightweight, standalone tool that improves dealing with SQL Server query plans so much, you’ll wonder why it hasn’t been incorporated into SSMS (and let’s face it, viewing plans in SSMS really sucks!).
There are several ways to open a plan: In SSMS, right-click a graphical plan and select “Show Execution Plan XML”, then copy and paste the plan XML into Plan Explorer. Or, save an execution plan from SSMS to a .sqlplan file, then open the file from Plan Explorer.
Download SQL Sentry Plan Explorer here.