It's not available yet, but the Mono project team are working on an Ahead of Time compiler that will do what you are looking for. The intention is for Mono to work on the iPhone (like Unity) but it should work for all platforms.
Edit: It does support Mono x86, but I'm not sure if they have included the feature that packs in dependent classes yet (though from an interview I heard, it's planned)
Edit 2: Including dependencies is currently supported, thanks Dykam!
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