Is there a way to add a url(not to the file itself) to assets? I am testing Craft to see if it would be a good fit for sites I build.  At this point, I do feel it is great and might fit most of the work I do.  The only thing I can't figure out is how I could add a url to images to build a logo gallery (ie: list of logos that link to the partners websites).

Is there a way to do this by default?  I can't find any information on it.
You can add any number of fields to your asset sources (just like you can for 'user groups', 'category groups', 'tag groups', or 'entry types'). Under 'settings > assets > sources', click a source (or create new); then click the 'field layout' tab and add your field (field needs to be created first); and save. For a url you would likely just use a textfield.

In your template you would access it with something like this:

{{ entry.myAssetsFieldHandle.first().myLinkUrlFieldHandle }}