SafeManuals offers product manuals for nearly 900,000 products. I tested five products in different categories using products in my home and SafeManuals had all of them. Currently, over 3,600 brands are listed on SafeManuals in hundreds of categories.
Some manuals are offered in multiple languages including: English, Spanish, Portugese, Chinese, German, Italian and French. The English on SafeManuals is very poor. I guess it doesn't matter as long as you can easily navigate the dropdown menus to find the product you need a manual for.
What makes SafeManuals interesting is that the manuals are all user-submitted. I don't think I've seen this before on a manual download site. Instead of SafeManuals doing the work to find the manuals, users submit them into the proper buckets for product, category and language.
There's a pretty neat widget which allows you to embed product manuals on your site. The widget can be customized to only show specific brands or products.