To block Facebook via DNS, block the following domains:
facebook.com
facebook.net
facebook.co.in
facebook.co.uk
fbcdn.com
fbcdn.net
fbsbx.com
fb.me
fb.com
To block via IP, have a look at this new project: banIP: new project needs testers & feedback
There you can block via ASN number, e.g. the primary ASN for facebook is 32934 - that's all to effectively block facebook via IP.