I had an XBox 360 with a 20GB hard drive and I've been installing and uninstalling games as I played more with one or the other. But lately as I've gotten more sports titles this got to be a pain as I wanted to play more than one in a short span of time. These days you can get a Microsoft 250GB hard drive for $119-$129 which is the same size as the one in the new XBox 360 slim. And yes, I know, it's overpriced compared to hard drives you can get. But I read about people having problems with those generic cheaper drives which don't always come with compatible transfer cords.
The official Microsoft one comes with the transfer kit and cord and couldn't be easier to transfer all your old data from your smaller drive to the larger one which needs to be done with the transfer cord before you install the new drive. The cord connects to the USB connection in the back of the XBox 360 and then to the new drive. You then put in the transfer disc and write from the old drive to the new. When done, you turn off your Xbox 360, take off the old drive and plug in the new drive.
I got mine just yesterday, and it took me less than 30 minutes to put in the new drive following the instructions. Yeah, it could be cheaper, but at about the price of two new games, I think it's worth it, and especially for those who still have the 20GB drive as I did.