Someone else made an important copyright point:
- Do they have written permission from their client to publish the logo on the site?
I worked for IBM, and one of our suppliers had used our logo on their site while not having permission. We asked him to take it down and he did. It could easily have been uglier than that, given there were NDAs involved. So you do need to ask.
As for how to show 100 logos.
- Grid on a separate single page
- Teaser grid & option to see more
- Paginated in a frame which fits on the margins of your main page
- Stock ticker style, have them roll through. (I don't like this idea, not a fan of motion on a page unless triggered by the user)
- As watermarks <- Something I saw recently. Use the logo as a watermark behind something else, just on the edge of the page. So logos would be clickable when hovered over, but not in the way otherwise. As there are a lot, consider a "zoom" where the mouse hovers.
- Use parallax scrolling to fit your 100 logos in a sidebar of 1/4 of the height. Have them scroll through much faster than the main content. This should attract attention as well.
As for giving weight to your argument
- Load times: Yslow
- Competitor analysis (has been mentioned, i know) See how others in same and other industries do this, and discuss what is pleasant or unpleasant about each approach.
- Standardised methods: check WordPress plugins and other ready-made tools to showcase clients, portfolios, etc...
But the biggest question I would have is. Are they shortcuts to case studies and work examples for each client, or just a boyscout collection of badges? This will factor in to how you'll want to display them. Links need to be clickable, and have some information like a project title. A boyscout badge collection, is just a photowall.