When users navigate to my site, I want it to display :
http://example.com
and not:
http://example.com/default.aspx
If you run your web site under IIS just launch IIS manager in Windows, then open your site in a tree and double click on Default documents icon. In opened window make sure that index.aspx setting exists, if doesn't put it in and move it up to the first one in a list.
Also there is a way to set up the default document via admin script (vbscript) like this:
set node=getObject("IIS://LocalHost/W3SVC/1/Root")
node.defaultdoc = "index.aspx" & "," & node.defaultdoc
node.setinfo