Aghh. How do you sit for hours in an office not doing anything. Too much energy!

Put on some good music or call a family member that you haven't talk for some time.
I don't know your job, but you have a great boss 
The main thing is, keep on not doing anything (bad)

If you truly have no work you can do, then why not take in a book of short stories?
But make sure you truly have NO work to do, as if you are at work and getting paid for it and not doing the actual work, that is theft.

I've had office jobs with nothing to do and found those were my biggest risks in terms of porn.

I would recommend setting strict rules as to which sites you are allowed to look at. its too easy to be looking at a news site, see the name of an actress (lets say) think "I wonder what movies she has been in" and then google her name. next comes the free pictures of her....

Also, I started using spare time to write in Microsoft word - that looks like you are working :-) Write a book, a diary, letters to your wife, whatever it may be. 

Post here!

Use Hebrewbooks to learn

Ask for more work! 

Hope those help.

Learn how to write VBA code in Excel.
I've seen once an excel sheet which acted as a facebook messenger chat, so you can chat on facebook (text only) while in excel so it seems like working.
The possibilities are endless, you can play games, and do other cool stuff in excel.

I don't recommend it, and I'm not a posek regarding company time stealing.

An important component in staying clean is to feel productive and good about yourself.  It may be that your boss did not assign you any work, but you should ask for work or even look for something you know needs to get done or will provide value for your employer.  This will acoomplished 2 things:

1.  It will keep you busy and feeling productive
2. It will improve your status with your employer, which can leads to better opportunities/work for you.

Hatzlacha! 

Some great suggestions guys. I'd take it a step further.

How about getting to know yourself a bit in your spare time? If we get focused we can accomplish a ton more with this amazing gift called life. Ask yourself questions: Who am I? What are my character strengths and weaknesses? What are my values? What do I want to accomplish? What goals - short and long term - can I make for myself? etc. Journaling daily can change one's life tremendously.

Once we start to experience life from an inner perspective it can get us much closer to Hashem and Yiddishkeit as well. Life in general just becomes more genuine and worthwhile. Our experience of life becomes much richer, deeper, fuller and oh.. soo much more fulfilling!

We have endless opportunity for growth in all aspects on this earth, and sadly we mostly don't even scratch the surface. We just 'exist' rather than 'live'. We go thru life by default, sort of forced or spaced out. Hashem gives us the opportunity to 'design' our lives to a great extent! We were not meant to exist in a low mode of life like animals. I believe that self-discovery, healing, and approaching life with a 'growth and accomplishment' mentality, drastically reduces temptation and lightens this struggle altogether. You are just functioning from a much higher level.

There is a paradox here, I believe. As challenged as we are by today's technology and the disintegration of true Torah dominance in our lives; the weakening of our resistance to external forces etc, etc. We also have a wealth of resources and opportunity for self discovery and growth like never before! Let's make use of that.