Most programmes and projects are subject to the Triple Constraints of budget, schedule and scope. It is the first of these constraints that we are discussing today. For your programme or project to be successful is has to stay within the approved budget. The approved budget can be either the original baseline budget or it can include approved changes. Even if the budget is only loosely constrained you want to track the actual expenditure for reporting purposes. This article describes some of the basic principles of budget management including forecasting, baselines, approved changes, actual expenditure and variance.
I just Googled across this great blog from Dick Billows covering a range of subjects on project management tools, techniques