You've a presentation or proposal for a corporate client and want to add a hint of your target audience's branding. You visit their Web site and find that every instance of their logo would need some heavy editing to get rid of background, toolbar bits, and so forth.
Instead, point your browser at Google Images and search for:
"company/project/product name" logo.
Replacing, of course, company/project/product name with the name of the company, project, or product you're after.
Google Images should return various versions, if it knows of any, of the corporate, project, or product logo. And, chances are, one of them is an unadulterated version on a plain white or black background. Here, for example, are results for
"o'reilly & associates" logo.
Save the image -- usually right mouse-click and Save Picture as... or the like -- and drag it right into your PowerPoint or Word document.