Sharepoint - Link on wiki page to Excel document that opens in Excel Online
Append Web=1 to the url to instruct it where to open. Of course you have to have all the prereqs in place.
/PWA/ProjectBICenter/Documents/AllXLDashboards.xlsx?Web=1
Opens it in Excel Services web page
/PWA/ProjectBICenter/Documents/AllXLDashboards.xlsx?Web=0
Opens it in excel