<p>I'm using BlogEngine.NET (a fine, fine tool) and I was playing with the TinyMCE editor and noticed that there's a place for me to create a list of external links, but it has to be a javascript file:</p>

<p><code>external_link_list_url : "example_link_list.js"</code></p>

<p>this is great, of course, but the list of links I want to use needs to be generated dynamically from the database. This means that I need to create this JS file from the server on page load.  Does anyone know of a way to do this? Ideally, I'd like to just overwrite this file each time the editor is accessed.</p>

<p>Thanks!</p>

If you can't change the file extension (and just return plain text, the caller shouldn't care about the file extension, js is plain text) then you can set up a handler on IIS (assuming it's IIS) to handle javascript files.
See this link -
http://msdn.microsoft.com/en-us/library/bb515343.aspx
-  for how to setup IIS 6 within windows to handle any file extension. Then setup a HttpHandler to receive requests for .js (Just google httphandler and see any number of good tutorials like this one:
http://www.devx.com/dotnet/Article/6962/0/page/3
)