From a recent Wall Street Journal article:
Create a special account. Don’t delay the inevitable. Create a separate account for the money you will be using to pay your taxes throughout the year. Choose a percentage of your revenue to set aside, and steadily make deposits in the account whenever money arrives.
Simple advice, but very true, and otherwise expressible as: “Do not resort to denial.” For a full breakdown on the tax issue and a sizeable dose of general freelance savvy, check out The Freelancer’s Bible, by Freelancers Union founder Sara Horowitz (“She’s like the history professor who lit a fire in our chests and made us think the world was ours to change.”).