ML2166 already listed a couple of links in order to get high quality logos.
However, Wikipedia is a quite source for logos as well.
For example:
1. Go to the page of the company, you're searching for; for example: http://en.wikipedia.org/wiki/Mercedes-Benz
2. Click on the logo of the the company (top right box)
3. A new page will appear; here:http://en.wikipedia.org/wiki/File:Mercedes-Benz_logo.svg
4. Right mouseclick on 2000px (a higher px-value is better) and choose "Save as..."
5. Rename "2000px-Mercedes-Benz_logo.svg" into "2000px-Mercedes-Benz_logo.png"
That's it! The best thing about those Wikipedia-logos: The background is transparent so it's easy to place those logos on your texture.
However, Wikipedia is a quite source for logos as well.
For example:
1. Go to the page of the company, you're searching for; for example: http://en.wikipedia.org/wiki/Mercedes-Benz
2. Click on the logo of the the company (top right box)
3. A new page will appear; here:http://en.wikipedia.org/wiki/File:Mercedes-Benz_logo.svg
4. Right mouseclick on 2000px (a higher px-value is better) and choose "Save as..."
5. Rename "2000px-Mercedes-Benz_logo.svg" into "2000px-Mercedes-Benz_logo.png"
That's it! The best thing about those Wikipedia-logos: The background is transparent so it's easy to place those logos on your texture.