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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@ Precursors - Didn't one of the books says that the Forerunners may have wiped them out? If that is true, and considering that the forerunner don't even know how to create a super weapon intelligently (yeah, destroy yourselves instead of destroying the Flood... makes total sense), that doesn't say much for the precursors.