Create a web part page but it's missing left Navigation

If you don't want to use javascript/jQuery, here's another way to get the left navigation back in web part pages.

1. Create a new web part page
2. Edit the page in SharePoint Designer
3. Remove custom css

Delete this code block:

<SharePoint:UIVersionedContent ID="WebPartPageHideQLStyles" UIVersion="4" runat="server">
<ContentTemplate>
<style type="text/css">
body #s4-leftpanel {
   display:none;
}
.s4-ca {
   margin-left:0px;
}
</style>
</ContentTemplate>
</SharePoint:UIVersionedContent>
<SharePoint:UIVersionedContent ID="WebPartPageHideQLStyles" UIVersion="4" runat="server">

4.-Remove the overrides for the left column

Remove all three lines:

<asp:Content ContentPlaceHolderId="PlaceHolderPageImage" runat="server"></asp:Content>
<asp:Content ContentPlaceHolderId="PlaceHolderNavSpacer" runat="server"></asp:Content>
<asp:Content ContentPlaceHolderId="PlaceHolderLeftNavBar" runat="server"></asp:Content>

Source: http://techmikael.blogspot.it/2011/08/adding-left-navigation-menu-to-web-part.html

If I use following method then I get both web part page and the left navigation.

Go to site actions-->More options-->Publishing Page. I selected "(Welcome Page) Blank Web Part page"

In SharePoint 2010, the left nav is inexplicably hidden in web part pages. You can’t just change the page layout for these pages as you can with page layout based pages that are stored in the /pages/ library (via the publishing feature).

<!– Turn on left navigation –>
<script type=”text/javascript”>
$(document).ready(function() {
$(“#s4-leftpanel”).show();
$(“.s4-ca”).css(‘margin-left’, ’155px’);
});
</script>