I found something that's really cool:
http://halo.bungie.org/misc/sloftus_scalecomparison/1280.html
This chart has scale comparisons to objects in Halo. It looks like it took a lot of work.
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Why the hell are the girls 6'1? I'm barely 6'3, and most girls I know fall somewhere in the range of 5'3-5'9