To start, Xerox recently announced their new line of green office paper. It's called High Yield Business Paper and it is considerably greener than traditional office paper. For example, normal office papers only use 45 percent of the tree they are milled from, wasting the rest. Xerox's new process uses 90 percent, meaning fewer trees need to be cut down. It is also produced using fewer chemicals, and it's milled in a plant that uses hydroelectric power. I am definitely going to suggest that my office start using this. It's only downside is that it can yellow over time...so maybe it's not suitable for contracts, or ultra important documents.
There are dozens of other companies that also sell green office products. TheGreenOffice.com is a good place to start...they have tons of office products (some conventional and non-green), but they very clearly specify which is which. They also offer a very specific carbon calculator for figuring out how much of an environmental impact your office has.
A simple Google search for "green office supplies" yields over 50 million results (some of which are probably not legit), but still...you have no excuse not to tone your environmental impact down...at least a little bit. :-)