Please note that because they are transparent PNG files they are displayed with a rather ugly black background. All images (thumbnails to medium size) will have this ugly black background except for the full size images. The full size images, when displayed, and when drug to your desktop (or downloaded via browser) will be completely transparent and should work with any colored background. I've also put up different colored versions and layouts of some (UW – as white and black, IO – both long and square format). The UW ones are a bit tricky in that the black logo looks like there's nothing there on the thumbnails/medium images, and the white shows up in the thumbnails/med but since it's white on white you don't see it at full res.
Let me know if you don't see a logo you'd like and I'll add it.