I had the same problem after knee surgery. My chiropractor actually helped me the most. Honest-to-God, cross my heart and all that, I know it sounds like something out of a medievel torture chambe, but it worked. He used a table that rocked me nearly upside down. After a week or so of that, it was on with the boots and I'd hang upside down from a horizontal pole for 10 or 15 minutes. That along with other therapies got rid of the excess fluid any time it popped up - which it did quite a bit in the first year.
Definitely keep up with the ice and leg elevation that Sandee described. You might also check with your doctor to see if he'll prescribe a Polar Care unit for you. I had one for both my shoulder surgeries and it made a world of difference. I used it for several months after surgery while I was doing physical therapy and any other time I just plain over-did it. Here's a link for some cold therapy products you can discuss with your doctor:
http://www.kneeshop.com/products.asp?cat=20
Here are some tips my Mom in law suggested as she has had the surgery herself...
To much time on your feet will cause excessive swelling and a slow down of the overall strengthening and conditioning of the affected leg.
Keeping your affected leg elevated is very important. How long to keep your leg elevated will vary between individuals, but in the first two weeks after surgery if you are not walking or exercising, the leg it should be elevated and it should be positioned higher then your heart for proper drainage of the area surrounding your knee.
Keeping ice on the knee is important as well. The ice is used for pain control and to decrease swelling. You really cannot overdue the ice. Many people will have questions on how often the ice should used and how long. Using ice immediately after exercise is the time its most effective along with foot elevation for edema control it will be the best one-two punch you can get to keep pain and swelling manageable.
If you are someone that retains fluid easily in the first place, your doctor may prescribe a diuretic like lasix to rid the body of the excess fluid