Someone "blocks" you on Facebook when he no longer wants you to be able to communicate with him using the site. "Blocking" is different from "unfriending," which simply removes you from his list of contacts. However, it's still possible to view the profile -- a truncated version of it, in nearly all cases -- of someone who blocked you on Facebook, albeit not while logged in to your Facebook account.
Log out of your Facebook account.
Navigate to your former friend's profile using his Facebook URL. Input his Facebook username in place of "username" in the Facebook URL form, facebook.com/username, in your browser's address box, then click "Enter."
Browse through his publicly available content, which varies depending on his Facebook settings. Note that you can't communicate with him in any way, be it via wall posts or direct messages.
Don't recontact someone who blocked you from Facebook unless you believe she did so in error, or you are close enough friends off the Internet to discuss the issue using other means. Contacting a Facebook user who has blocked you using the site -- namely, creating an auxiliary account to do so -- constitutes harassment and may result in you losing your site privileges.