I used a 5 gallon bucket (but as soon as I saw how tiny a base it made vs. my direcpc dish I decided to go different).
I got a 20 gallon "play" bucket. It is a big (blue) plastic bucket with rope handles (that you can usually find in either the yard supplies or mabey even the kids area).
I have more pictures up at my site
www.chrisrowland.com however at the moment the site is down (due to a problem with the hosting provider, I have emails in to them so it should be up later today).
Anyways with a bag and a half of cement in it (120lbs) I have yet to have it move at all. Also have had no problems with it moving (we have had 20-40 mph winds with storms and no movement whatsoever). The Rope handles are also very convenient whenever one has to drag it (you will not pick it up :>) across the yard to reposition the dish.
I also drilled small holes so that the water (rain) will drain from the dish. The first time it stormed I had about 8 inches of water in the thing (it's positioned next to a runoff point for the house). We are planning on planting flowers around it (we thought about ivy of some sort and letting it climb up the pole but I decided I didnt want to have to work to keep it cut back).
Pics are below.
The first pic is the dish mounted in a 5 gallon bucket (with the 20 in the background)
2nd is the 20 gallon -w- dish (how it is currently setup).
3rd is dish mounted in the 5 gallon (very top heavy).