As the name says, Instant Logo Search is a place where you can go to search for logos, and get results instantly. The site then gives you two options — SVG and PNG — and you can download the file(s) by clicking a link and moving on. You can also add logos to a bucket, then download them in a batch afterwards.
Now this site doesn't have every logo on the planet (McDonald's, for example, wasn't there when I searched), but it does have enough to become entirely too useful.
Another great Resources :
- http://www.brandsoftheworld.com/ is a great resource for eps files. Have to double check for most up to date version sometimes, and don't have every logo, but they have a lot!