Of the above solutions , though robust - they will deal with working your way around visual studio. I had exactly the same kind of requirement a year back and it was addressed like this :-
A global top navigation that is consistent across all site collections and different web applications.
Secondly, the link management was in a way that whenever a new link is added or existing link is modified, it happens only once and the change is reflected in top navigation across the entire site collections and web applications in the farm.
No webpart or wsp was created to achieve the same.
These were the exact stepsto achieve the same:-
A primary site collection on web application running on port 80 was decided to be landing area for the users. Lets call it
http://myportal/
We have created xml file known as portalnav.xml uploaded in the pages library of http://myportal
. This contains the defined navigation and their respective url. A sample of the same is mentioned in the screenshot below

We needed to add a XML datasource to the masterpage named portal.master and bind the sharepoint top navigation to this datasource.
<SharePoint:XmlUrlDataSource runat=server id=XmlUrlDataSource1 selectcommand=``http://myportal/Pages/portalnav.xml
AuthType=Basic AuthUserName=domain\userid" AuthPassword=enter the password of the site administrator here/>
<SharePoint:AspMenu
ID=TopNavigationMenuV4
Runat=server
EnableViewState=false
DataSourceID=XmlUrlDataSource1
AccessKey=<%$Resources:wss,navigation_accesskey%>
UseSimpleRendering=true
UseSeparateCss=false
Orientation=Horizontal
StaticDisplayLevels=2
MaximumDynamicDisplayLevels=5
SkipLinkText=
CssClass=s4-tn>
<DataBindings>
<asp:MenuItemBinding DataMember=Menu TextField=text ValueField=text NavigateUrlField=url
/>
<asp:MenuItemBinding DataMember=SubMenu TextField=text NavigateUrlField=url
ValueField=text />
</DataBindings>
</SharePoint:AspMenu>
<SharePoint:DelegateControl runat=server ControlId=TopNavigationDataSource Id=topNavigationDelegate>
<Template_Controls>
<asp:SiteMapDataSource
ShowStartingNode=False
SiteMapProvider="SPNavigationProvider"
id="topSiteMap"
runat="server"
StartingNodeUrl="sid:1002"/>
</Template_Controls>
</SharePoint:DelegateControl>
</asp:ContentPlaceHolder>
</asp:ContentPlaceHolder> `
- Once this xml file is published and approved , apply the changes to the masterpage and apply this masterpage(portal.master) across any site collections across the entire farm. It should work just fine.
The logic behind this is fairly simple -
1) An XML Datasource binded to the sharepoint default top navigation.
2) The path of the datasource is referred by all the site collections through the masterpage and authenticated by the primary site collection(http://myportal
) administrator's user account.
3) This way it is a centrally located and managed navigation however with security concerns as the credentials are passed in plain text. Since only farm admins have access to the site settings in our case, this was given a green flag from the security standpoint.