Slideshop.com has more than 1000 templates for download. You purchase slides sets which have 10-30 slide templates. Each set costs about $30 but there's a special 30% on the site now. Sign up for the newsletter and get a free slide each week. You can also download a sampler pak with lots of good example. You can easily customize the templates to work with your corporate branding.
Check it out: http://slideshop.com/