If you have a scanner, scan bills or other documents you might want to keep as you get them. At the end of the year, you can make a CD that has all important documents on it, labelled with that year, instead of having a huge filing cabinet.
Mark all the clothes in your closet with a clothespin, a safety pin, or some other mark. After six months to a year, donate whichever clothes you haven't used unless there is a good reason to keep them (formal wear for special circumstances, sentimental value, etc.).
Also, what websites or services have you found to be helpful in your decluttering or simplifying goals? I know www.flylady.com gets tossed around a lot, and at least one friend has found www.paytrust.com to be helpful in simplifying bill paying. Many people have been really successful in using FreeCycle as a way to less wastefully declutter.
Are there other sites or services you have found helpful? If so, please comment and I will try to get links up for them at some point soon.