Hard to tell.
Including Protheans and Forerunners
and Mass Relays and Rings (LOL)
Edit: Precursors too...
Edit 2: ALL OF THE STUFFS IN THE UNIVERSES EVEN TREES
[Edited on 03.25.2012 2:43 PM PDT]
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As much as I like ME, I'm going to have to go with Halo.