Buy Now or Wait?

When is the best time to buy a new computer?

I am interested in putting together my first desktop build ($1500 to $2000 range).

I realize that the longer you wait the more computer you will get for your money. But, is there a time of the year when hardware tends to be cheaper, or when the best deals can be had?

I am considering either buying one this week or waiting till Christmas?

Thanks for your input!