The best resource for unbiased CMS information is the CMS e-mail list, www.cms-list.org. Recent archives for the list are unavailable as of this writing, but take my word for it—the list is an invaluable look at the CMS market, including proprietary and open-source products.
The CMSWatch web site (www.cmswatch.com) combines expensive reports with free advice, summaries and introductions. It's a useful site when looking for information about CMS software.