Looking for an editable copy of a major logo? Brandsoftheworld.com has a large collection of logos for pretty much any company or product you can think of, ready to download in EPS format.
Of course, it's pretty easy to track down any company logo via Google Images, but the chances of finding a high-resolution version are somewhat slimmer, even if you choose the 'large files' option. The search functionality on the site is a bit basic — there's no preview, so for a brand with multiple potential logos you'll have to click through to find the one you want. Before you can download the files, you get a relatively stern warning about not using the logos for commercial use. Thanks Kaan!