There are several and different ways for doing exactly what you want. Indeed there a lots!
However, what I would really suggest you IS NOT TO DO IT! DON´T DO IT AT ALL!
It is obvious that if the IT guys (as I am) blocks such contents (as I also block), they can very easily discover what you are doing using the called "anonimous surfing". This is mainly prohibited on most companies, and usually such behave is punished with the lost of your job position.
Note that I´m not putting any comment about the behave itself, but I strongly disincorage you. I personally wouldnt. A few days ago, I found a employee that was accessing his personal computer home and from there accessing MSN and other stuff. He is no longer at the company.....
Facebook and other social networking sites are mostly blocked in some offices and schools. You can easily access this sites with ease by using OpenVPN connection. This is very easy to use and you don't need to pay something just to use this high secure Free VPN service to unblock all the restricted sites in your location. BUT REMEMBER this might be the best way to unblock some restricted websites but I hope you will use this with consent from your IT department or supervisors, this could end up you in hot water and out of your job.