Is there syntax highlighting for assembly in Sublime Text 2?

There is now a much better answer to this:

In Sublime Text, just go to Preferences > Package Control > install packages. Once there search for "mips-syntax" and hit enter on the result.

Once it installs you should be able to select MIPS as the syntax highlighting for whatever file you're editing.

Edit: Of course, this does assume that your Sublime has Package Control. You can get package control to do this and more at: http://wbond.net/sublime_packages/package_control

I've found another one Assembly x86 syntax definition.

It seems that this guy had done a huge amount of work, and keeps the syntax updated. At least at the time of writing the last change was 9 days ago.

He has also this post on Sublime forum.

No, but since Sublime Text 2 can read Textmate language definition files (.tmLanguage files), you could easily add support to Assembly by copying something like https://github.com/foxostro/x86-assembly-textmate-bundle to your "Packages" directory (C:\Users\hugo\AppData\Roaming\Sublime Text 2\Packages on my Win7).