Url rewriting
If you have a large website that you need to be google indexable (Googlable if I may coin a new phrase). Then it is worthwhile converting standard links such as myPage.asp?x=1&y=2 to someting like /web/x/1/y/2/myPage.asp where the "folder structure" translated back to a standard querystring before it is processed.
You can do this though .NET by writing a class that implements IHttpModule, however for added performance you should use an ISAPI filter. My personal favourite is UrlReWrite by Smalig software.
The only catch with using url-rewrites the new ‘virtual’ folder structure can lead to a heap of bad links. In this case you have to use <base href> to correct this.
I used it on three new sites www.listofdevelopers.info www.listofEstateAgents.info and www.listofschools.info