We almost get an answer here: Sublime Forum โ€ข View topic - New to Sublime - A few questions, but the first step is a little over-simplified.

1. Look in the asp folder for .tmLanguage files. There will be a fileTypes key. Add aspx as a value.

That folder with tmLanguage files is, on Windows 7, likely somewhere like here:

C:\Users\Your.Username\AppData\Roaming\Sublime Text 2\Packages\ASP

Then the file you want to edit is HTML-ASP.tmLanguage.

<array>
  <string>asp</string>
  <string>aspx</string>
 </array>

Add that second entry, close and reopen your aspx file, and poof, aspx is happy. Hope I didn't post that earlier, b/c that would mean I was too stupid to look it back up on my own blog. But I probably have.

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