Check out www.glassdoor.com to get reviews and salaries on over 11,000 companies. Reviews and salaries are posted by employees. It’s free but requires registration.
With their “give-to-get” model, just give them your review of a current or former employer (your post is anonymous — you don’t even need to include your job title) and get full access to all reviews for all companies.
It’s a fairly new website. So far we like it.