There actually is a formula that dictates the increase and decreases in this game. Better minds then mine have figured it out and while the changes may happen a day later than they have been predicting, they were spot on in their predictions last week. They have indicated that the following will happen shortly after midnight British time tonight.
Price Increases
Deco Chelsea
Agbonlahor Aston Villa
Geovanni Hull City
Wheater Middlesbrough
O'Brien J Bolton
Arteta Everton
Djourou Arsenal
Prices Decreases
Carrick Man United
Ballack Chelsea
Smith Newcastle
You don't want to make transfers just to pick up an extra point here and there, but if you are thinking about bringing in or getting rid of any of these players you may as well benefit from the price change. Plus building up your team value helps later on when you may want to bring in a player that is on the expensive side.