Andy Patrick, an ex-Rare developer of Kameo and Viva Pinata fame, has started blogging about his adventures making a game with the XNA Framework.
His first couple of posts have some great advice about the importance of building good debugging support into your game engine. I can second his experience of having taken such things for granted until I one day had to work on a game without them!
In fact I suspect this philosophy of working smart and building tools to save yourself time is one of the biggest differentiators between great and merely ok games, far more than the shader wizardry and optimization tricks that usually get all the attention.