There are a number of options available for you to use the first one I would mention is Master Pages if you going to use asp.net.
ASP.NET MVC uses layouts with the Razor view engine so you can control the page a bit more, I really like the MVC way of doing things as it keeps things simple in terms of your functionality and presentation.
Another option is the server side include (this is old fashioned and not really good):
<!-- #INCLUDE FILE="includeMe.html" -->
If you wanted to keep it as an html page you could 'hack' around in IIS to make html pages work with SSI but it is not a very good way of doing things.
Another way of providing information is by using jQuery to include snippets of html for your page to use, something like this, (sorry I haven't tested):
$("#destination-container").load("sourcepage.htm #content-in-this-page");
Again this is probably not the best way of doing things but you can use it for quick results.
My advice is to create a main page, whether it be a master page or a variation of one if you decide to go the MVC route then use PartialViews or something similar.
And of course look at the link Alex K provided: ASP.NET equivalent of server side includes