Here are all the Aperture Logos from the Portal series, vectored and in .ai and .svg format
There is some discrepancies from these, and what you might see on other computers, as the images were adjusted to have appropriate proportions.
Edit - version 1.2 - I recently became aware of another Aperture Science logo, this one seen only on Chell's jumpsuit. I also added the complete Aperture logo. I also edited the 1945 Aperture Science very slightly to more accurately reflect the in game logo.
Edit - NOTICE - this image has been lifted and placed on Reddit, Memebase, and other sites without my permission.